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Geode Cake

I finally hopped on the geode cake band-wagon this weekend, and am happy to report that this stunning design is a lot easier to make than you might think!

All you need is a frosted cake, clear rock candy, gel food coloring, and a some clear extract or alcohol!

This cake was inspired by an amazing amethyst/geode wedding cake made by Intricate Icings Cake Design. To help the purple pop even more, I added a silver border with edible art paint.

I modified the design to make it a bit more approachable for all of us home bakers!

image of a geode cake made with rock candy and edible gel food coloring paint to look like an amethyst

Making this Geode Cake: Step by Step Tutorial

Let’s walk through each step of this cake together to make sure it turns out as amazing as possible!

Step 1: Bake and Trim Your Cake Layers

Line four 7-inch round cake pans with parchment rounds and grease with non-stick baking spray or homemade cake release. 6-inch pans work too, the cake will just be slightly taller!

Divide the cake batter evenly between the prepared pans and bake for 33-36 minutes or until a skewer comes out with a few moist crumbs. Let them cool for 10 minutes, then run an offset spatula around perimeter of the pan to separate the cake from the pan. Flip the cake layers onto a wire rack to finish cooling.

Once the cake layers are fully cooled, use a serrated knife to level the tops of 3 of the layers before you assemble your cake. You can also wrap and freeze them in you’re making them in advance.

If you make these cake layers in advance and freeze them, let them thaw for about 20 minutes before making your cake. The cake layers should still be slightly cold to the touch, which will make it easier to assemble your cake.

Step #2: Make the Buttercream Frosting

While the cake layers bake and cool, make the vanilla buttercream frosting. You can use either an electric hand mixer or a stand mixer.

If your frosting seems too thick after mixing together all your ingredients, add in additional cream (1 teaspoon at a time). Or if the frosting is too thin, add in more powdered sugar (1/4 cup at a time).

If you’re unsure how thick your frosting should be, you can learn what consistency you’re looking for in my frosting consistency post.

image of vanilla american buttercream in bowl that's been stirred with a spatula to make it super smooth

Step 3: Stack and Crumb Coat the Cake Layers

Next it’s time to assemble the cake! I recommend freezing your cake layers for about 20 minutes before stacking them. It will make them was easier to handle and frost.

Stack and frost the cake layers on a 10-inch greaseproof cake board. Use a dab of frosting to help stick the bottom cake layer to the board.

Spread an even layer of frosting between each cake layer with an offset spatula. Place the unleveled cake layer on top, to give the cake a rounded top.

Smooth with a small offset spatula and/or acetate sheet, then chill the cake in the fridge (30 minutes) or freezer (10 minutes) until the frosting is firm to the touch.

image of purple cake layers being stacked and crumb coated

Step 4: Cut Out a Section of the Cake

Once the cake is chilled, used a sharp knife and spoon to cut out a large section from one side of the cake. This can be as small/large, or shallow/deep as you want!

I like to keep mine pretty shallow so that I’m not removing too much cake, but you can create whatever shape you want.

image of a cake being cut into to make a geode cake

Cover the cut out section with a layer of white buttercream.

Step 5: Add the Second Layer of Frosting

Color the remaining buttercream grey by mixing in a few drops of black gel food. Add a second, thicker layer of grey frosting around the cake, avoiding the cut out section. Use an offset spatula or acetate sheet to create a texture look that resembles a rock.

Press bits of rock candy into the cut out section until it is fully covered.

image of rock candy being pressed into a cake to make a geode cake

Step 6: Color the Rock Candy

Combine 1 Tbsp of clear extract or liquor with a generous squirt of gel food coloring. Stir the mixture until it’s combined, then use a clean paint brush to paint the rock candy.

I used purple gel food coloring to make an amethyst, but you can make this any color or make an ombre pattern of you want!

image of a geode cake made with rock candy and edible gel food coloring paint

Step 7: Add the Finishing Touches

This last step is optional, but you can paint the edge of the geode with edible silver or gold paint to really make it pop!

Geode Substitutions and Swaps

Below are some swaps and substitutions that can be made in this marble cake recipe.

  • All Purpose Flour – This recipe turns out best with AP flour, but you can use a gluten free flour blend or cake flour if that’s all you have on hand.
  • Granulated Sugar – I do not recommend reducing the amount of sugar or changing the type of sugar, as it will change the texture of the cake layers.
  • Buttermilk – You can also use full fat yogurt, sour cream, whole milk, or an alternative yogurt or milk (almond, soy, oat) if you’re dairy free.
  • Egg whites – You can use 4 whole eggs in place of the egg whites in this recipe. Or if you have an egg allergy you can use a flaxseed egg or vegan egg replacer.
  • Vegetable Oil – You can use any flavorless oil in this recipe, so canola or even sunflower oil would work great!
  • Unsalted Butter – If you only have salted butter on hand you can use it in place of the unsalted butter in this recipe. Just be sure to omit the salt that this frosting recipe calls for. You can also use vegan butter in its place!
  • Heavy Cream – Whole milk or alternative milk (soy, almond, oat) will work fine in this frosting recipe if that’s what you have on hand.

Tips for Making The Best Geode Cake:

  • Be sure to properly measure your flour (spoon into the cup measure, then level) or use a kitchen scale to measure your dry ingredients.
  • Ingredients at room temp mix together better, so be sure you set out any cold ingredients ahead of time.
  • Mix your cake batter just until the ingredients are incorporated. This will ensure your cake layers are tender and soft.
  • Chill your cake layers in the freezer for about 20 minutes before assembling the cake. This makes it easier to stack and frost.
  • Make this geode cake vegan or dairy free if needed! Use your favorite type of dairy free milk to replace the buttermilk and heavy cream, and use vegan butter sticks in place of the butter. For the eggs I recommend using an egg replacer like this.
image of chelsey white of chelsweets with her amethyst geode cake

Making This Geode Cake In Advance & Storage Tips:

  • Make your cake layers in advance and freeze them. It breaks the process up and make it more approachable.
  • Make your frosting ahead of time too, or save any leftover frosting! It can be stored in an airtight container in the fridge for up to a month, or in the freezer for up to 3 months. Be sure to give it a good stir once it thaws to get the consistency nice and smooth again.
  • A frosted cake can last in the fridge for up to a week. The buttercream locks in all the moisture, keeping the cake fresh and delicious!
  • If you cut into the cake and have leftovers, use any remaining frosting to cover the cut section to keep it moist and store in the fridge for up to a week.

Other Recipes You Might Like:

Let Me Know What You Think!

If you make this geode cake, I’d love to hear what think of it! Let me know by leaving a rating below.

If you plan to share on social media, you can tag me @chelsweets! Also use #chelsweets so that I can see your amazing creations on social media.

Yield: 24

Geode Cake

image of a geode cake made with rock candy and edible gel food coloring paint

This geode cake is surprisingly easy to make! With the help of some rock candy and food coloring, your cake will look just like a stunning amethyst!

Prep Time 30 minutes
Cook Time 33 minutes
Additional Time 30 minutes
Total Time 1 hour 33 minutes

Ingredients

Vanilla Cake Recipe

  • 3 cups all-purpose flour (390g)
  • 3 cups granulated sugar (600g)
  • 2 1/2 tsp baking powder (10g)
  • 1 tsp salt (6g)
  • 1 cup unsalted butter, room temp (226g)
  • 1 cup egg whites from a carton or about 7 egg whites, room temp (235g)
  • 1 1/2 cups buttermilk, room temperature (345g)
  • 2 Tbsp vegetable oil (30g)
  • 2 tsp vanilla extract (8g)
  • purple gel food coloring - if desired

Vanilla Buttercream Frosting

  • 2 cups unsalted butter, room temperature (434g; 1 lb box)
  • 1 Tbsp vanilla extract(12g)
  • 1/2 tsp salt (3g)
  • 7 cups powdered sugar (907g; 2 lb bag)
  • 3 Tbsp heavy cream or whipping cream (45g)
  • black gel food coloring

Decorations

Instructions

Vanilla Cake Layers:

  1. Preheat oven to 350°F. Line four 7" or four 6" pans with parchment rounds, and grease with non-stick baking spray.
  2. Mix together 3 cups all purpose flour, 3 cups sugar, 2 1/2 tsp baking powder and 1 tsp salt in a stand mixer with a paddle attachment or hand mixer until fully combined.
  3. Mix in 1 cup of unsalted butter slowly into the dry ingredients on a low speed. Continue to mix until no large chunks of butter remain and the mixture looks crumbly.
  4. Pour in 1 cup of egg whites and mix on low until just incorporated. Mix in 1 1/2 cups buttermilk in two installments, on a low speed.
  5. Add in 2 Tbsp of vegetable oil and 2 tsp of vanilla extract and mix at a low speed until fully incorporated.
  6. If you plan to color your cake layers, add in the gel food coloring with the vanilla and oil. I like to color the cake layers to made the color of the geode, but this is optional.
  7. Scrape down the sides of the bowl with a rubber spatula, then beat on a low speed for about 30 seconds to make sure everything is properly mixed together.
  8. Divide the batter evenly between your prepared pans.
  9. Bake for 33-36 minutes or until a toothpick comes out with a few moist crumbs.
  10. Allow the pans to cool for 10 minutes, then run a small offset spatula around perimeter of the pan to separate the cake from the pan.
  11. Place cake layers into the freezer for 30 minutes to accelerate the cooling process. Once the layers are fully cooled, carefully flip the pans and remove the layers.
  12. Use a serrated knife to level the tops of 3 of the layers, leaving 1 unleveled. You can wrap and freeze them in you're making them in advance.
  13. If you make these cake layers in advance and freeze them, let them thaw for about 20 minutes before making your cake. The cake layers should still be slightly cold to the touch, which will make it easier to assemble your cake.

Vanilla Buttercream Frosting:

  1. Beat 2 cups of unsalted butter on a medium speed for 30 seconds until smooth with a paddle attachment / stand mixer or a hand mixer.
  2. Mix in 1 Tbsp vanilla extract or vanilla bean paste and 1/2 tsp salt on a low speed.
  3. Slowly add in 7 cups of powdered sugar while mixing slowly on the lowest setting. Half way through add in 3 Tbsp of heavy cream or milk to make it easier to mix. I like to place a kitchen towel over my mixer to contain any powdered sugar clouds.
  4. Mix on low until the ingredients are fully incorporated and the desired consistency is reached. 
  5. If the frosting is too thick, add in additional cream (1 Tbsp at a time). If the frosting is too thin, add in more powdered sugar (quarter of a cup at a time).
  6. Wait to color the buttercream until the cake is filled and crumb coated.

Assembling this Geode Cake:

  1. Stack and frost cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board.
  2. Add an even layer of buttercream between each cake layer with a large offset spatula. Place the non-leveled cake layer on top to give the cake a rounded top.
  3. Add a thin coat of frosting around the cake, fully cover the cake layers.
  4. Smooth using a bench scraper, then chill the cake in the fridge (20 minutes) or freezer (5 minutes) until the frosting is firm to the touch.
  5. Once chilled, used a sharp knife to cut out a large section from one side of the cake. This can be as small/large, or shallow/deep as you want! I like to keep mine pretty shallow so that I'm not removing too much cake, but you can create whatever shape you want.
  6. Cover the cut out section with a layer of white buttercream.
  7. Color the remaining buttercream grey by mixing in a few drops of black gel food. Add a second, thicker layer of grey frosting around the cake, avoiding the cut out section. Use an offset spatula or acetate sheet to create a texture look that resembles a rock.
  8. Press bits of rock candy into the cut out section until it is fully covered.
  9. Combine 1 Tbsp of clear extract or liquor with a generous squirt of gel food coloring. Stir the mixture until it's combined, then use a clean paint brush to paint the rock candy. I used purple gel food coloring to make an amethyst, but you can make this any color or make an ombre pattern of you want!
  10. This last step is optional, but you can paint the edge of the geode with edible silver or gold paint to really make it pop!
  11. Either enjoy the cake immediately, or store in the fridge for up to a week! If you refrigerate the cake, take it out an hour or two before you want to cut into it, to allow it warm to room temperature.

Notes

Make your cake layers in advance and freeze them. It breaks the process up and make it more approachable.

Make your frosting ahead of time too, or save any leftover frosting! It can be stored in an airtight container in the fridge for up to a month, or in the freezer for up to 3 months. Be sure to give it a good stir once it thaws to get the consistency nice and smooth again.

A frosted cake can last in the fridge for up to a week. The buttercream locks in all the moisture, keeping the cake fresh and delicious!

If you cut into the cake and have leftovers, use any remaining frosting to cover the cut section to keep it moist and store in the fridge for up to a week.

Nutrition Information

Yield

24

Serving Size

1

Amount Per Serving Calories 527Total Fat 26gSaturated Fat 15gTrans Fat 0gUnsaturated Fat 9gCholesterol 65mgSodium 263mgCarbohydrates 70gFiber 0gSugar 58gProtein 5g
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