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image of a vanilla cake that's filled with a white chocolate mousse cake filling
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4.92 from 47 ratings

White Chocolate Mousse Cake

This white chocolate mousse cake recipe is made with fluffy white cake layers, the fluffiest white chocolate mousse filling, and a decadent white chocolate buttercream.
Prep Time15 minutes
Cook Time35 minutes
Additional Time20 minutes
Total Time1 hour 10 minutes
Course: Cakes
Cuisine: American
Servings: 24
Calories: 748kcal
Author: Chelsey White

Ingredients

White Chocolate Mousse

  • 1 1/3 cups good quality white chocolate chips 215g
  • 1 1/2 cups heavy cream or heavy whipping cream, cold - divided 360ml
  • 1/4 cup powdered sugar 30g
  • 1 tsp vanilla extract or vanilla bean paste 4mL
  • pinch fine salt less than 1/8 tsp

White Cake Recipe

  • 1 cup (2 sticks) unsalted butter, room temperature 226g
  • 3 cups granulated sugar 600g
  • 1 cup carton egg whites or 7 large egg whites, room temperature 235g
  • 3 cups cake flour 360g
  • 2 1/2 tsp baking powder 10g
  • 1 tsp fine salt 6g
  • 1 1/2 cups full-fat sour cream, room temperature 380g
  • 1/4 cup vegetable or canola oil 56 ml
  • 1 tsp vanilla extract or vanilla bean paste 4ml

White Chocolate Buttercream Frosting

  • 2 cups unsalted butter, room temperature 452g
  • 7 cups powdered sugar 900g
  • 1 tsp vanilla extract or vanilla bean paste 4ml
  • 1/2 tsp fine salt 3g
  • 1/3 cup heavy whipping cream, room temperature 75g
  • 1 cup white chocolate chips, melted and cooled 160g

Tools and Equipment Needed

Instructions

White Chocolate Mousse Filling

  • Make the white chocolate mousse first, so it has time to chill. Or better yet, make this mousse in advance! It can be made 1-2 days ahead of time.
  • Add the white chocolate chips and 1/2 cup heavy cream in a medium-sized, heat-proof bowl. Heat for 60-75 seconds in the microwave, then let the mixture sit for a minute. Stir until combined with a rubber spatula. The white chocolate should be completely melted, and the mixture should be smooth. If you don't have a microwave, you can also use a double boiler. Set aside.
  • Add 1 cup of heavy cream, powdered sugar, vanilla extract, and a pinch of fine salt in a large bowl or the bowl of a stand mixer fit with a whisk attachment.
  • Mix on medium-high speed until the whipped cream starts to gather in the whisk attachment and you can see texture around the edge of the bowl. The whipped cream should be thick and able to keep its shape. This usually takes about 2 1/2 to 3 minutes in my stand mixer.
  • Gently fold half of the whipped cream into the white chocolate cream mixture using a rubber spatula. At this point, the white chocolate mixture should have cooled down a bit and should still be fluid but shouldn't be hot to the touch. Use the spatula to swoop around the sides of the bowl and pull through the center like I show in the video of this recipe. Fold in the remaining half of the whipped cream. Be careful not to over-mix the mousse, or it will become deflated and lose its structure.
  • Cover the mousse with plastic wrap and chill in the refrigerator for at least 2 hours.

White Cake Layers

  • Preheat oven to 325°F. Line and grease four, 7-inch pans or three, 8-inch cake pans with parchment rounds.
  • Add the unsalted butter and granulated sugar into the bowl of a stand mixer. Mix together on a high speed with a whisk attachment for a few minutes. Scrape down the sides of the bowl as needed with a rubber spatula. The mixture should become lighter in color as air is whipped into it.
  • Add in the room-temperature egg whites and mix at a medium speed until they're incorporated.
  • Whisk together the cake flour, baking powder, and salt into a separate bowl.
  • Add half of the dry ingredients into the butter mixture and mix on a low speed until incorporated.
  • Add the sour cream, oil, and vanilla extract and mix at a low speed until combined. Scrape the sides and bottom of the bowl as needed.
  • Mix in the remaining dry ingredients on a low speed.
  • Divide the batter evenly between the prepared cake pans. I like to use a digital kitchen scale to weigh my pans to make sure my layers bake up to be the same height.
  • Bake for 37-40 minutes, or until a toothpick comes out with a few moist crumbs. Rotate the pans halfway through to help them bake evenly.
  • Allow the pans to cool for 10 minutes, then run an offset spatula around the perimeter of the pan to separate the cake from the pan.
  • Place the cake layers into the freezer for 45 minutes to accelerate the cooling process. Once the layers are fully cooled, carefully flip the pans and remove the layers from the pans.
  • Use a serrated knife to level the tops and trim the sides to remove any caramelization.

White Chocolate Buttercream Frosting

  • While the cake layers bake and cool, make the white chocolate buttercream frosting.
  • Beat the butter on a low speed for 30 seconds with a paddle or whisk attachment until smooth.
  • Add in the vanilla extract and salt and beat on a low speed.
  • Slowly add in the powdered sugar and mix on a low speed. Add in the heavy cream halfway through to make the frosting easier to mix.
  • Mix in the melted and cooled white chocolate on a low speed and scrape down the sides and bottom of the bowl with a rubber spatula as needed.
  • Continue to mix until the ingredients are fully incorporated and the desired consistency is reached. 
  • If the frosting is too thick, add in additional cream (1 teaspoon at a time). If the frosting is too thin, add in more powdered sugar (a quarter of a cup at a time).
  • Stir by hand with a rubber spatula to make the frosting extra smooth, then place the frosting in a large piping bag. Seal the top of the bag with a rubber band or clip and cut an opening that's about 3/4 inch wide at the base of the bag. Set aside.

Assembling This White Chocolate Mousse Cake

  • Stack and frost the cake layers on a greaseproof cake board using a dab of frosting to help stick the first cake layer to the board.
  • Pipe a ring of buttercream around the perimeter of each cake layer, then spread an even layer of white chocolate mousse inside the ring. Use about 1/3 of the mousse between each layer if you have 4 cake layers. If you have 3 cake layers, use 1/2 of the mousse between each layer.
  • Repeat with the remaining cake layers. Once all the cake layers are stacked, spread a thin coat of frosting around the cake to fully cover the cake layers. If your layers are sliding around, insert a chopstick or wooden dowel into the center of the cake to make it more stable.
  • Smooth using a bench scraper, then chill the cake in the fridge (30 minutes) or freezer (10 minutes) until the frosting is firm to the touch.
  • Add a second, thicker layer of white chocolate frosting to the cake and smooth using an icing comb.
  • Decorate as desired! I chose to add some buttercream swirls piped with a Wilton 1M frosting tip along with a pretty sprinkle blend.

Video

Notes

Tips for Making the Best White Chocolate Mousse Cake

  • When making the white chocolate mousse, chill your mixing bowl and whisk attachment in the freezer. It makes it easier and quicker to whip up the whipped cream for the mousse.
  • Properly measure your flour (spoon into the cup measure, then level). Or better yet, use a kitchen scale to measure your dry ingredients.
  • Mix your cake batter just until the ingredients are incorporated. This will ensure your cake layers are tender and fluffy.
  • Use a scale to weigh your cake pans as you fill them. This will make your cake layers bake to the same height and bake more evenly.
  • Bang your cake pans on the counter before putting it in the oven. This brings any air bubbles that are trapped in the batter to the surface.
  • Level your room temperature or thawed cake layers with a serrated knife to make them easier to stack.
  • Chill the leveled cake layers in the freezer for about 20 minutes before assembling the cake. It makes it so much easier to stack and frost them!

Making This Cake in Advance and Storage Tips

  • Make your cake layers in advance and freeze them. It breaks the process up and makes 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.
  • The white chocolate mousse filling in this cake can be made up to two days in advance if stored in an airtight container in the fridge.
  • A frosted cake can last in the fridge for up to a week, or in the freezer for up to a month. 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

Serving: 1 | Calories: 748kcal | Carbohydrates: 86g | Protein: 6g | Fat: 44g | Saturated Fat: 25g | Polyunsaturated Fat: 16g | Cholesterol: 106mg | Sodium: 280mg | Sugar: 71g