Make the chocolate ganache first, because it needs time to cool and thicken before it's used to frost this cake.
Heat 1/4 cup of heavy cream in a heatproof bowl in the microwave for 15-30 seconds, until it's just beginning to bubble.
Gently pour 1/3 cup of dark chocolate chips into the heavy cream. Make sure the chips are fully covered with cream. Let the mixture sit for 1 minute. If you want to use milk chocolate to make the ganache, use 1/2 cup or 85 grams of milk chocolate.
Stir slowly until the cream and chocolate are combined and the mixture is smooth. If any bits of chocolate aren't fully melted, heat the mixture again for 15 seconds and stir until smooth.
Mix in 1 Tbsp of unsalted butter, 2 tsp of corn syrup (optional), and 1/4 tsp fine salt until combined.
Cover with plastic wrap to prevent the ganache from forming a skin, then set aside to cool to room temperature. If you need to make this in advance, it can be covered and stored in the fridge for up to a month.
Chocolate Simple Syrup - Optional
Pour 1/4 cup water and 1/4 cup granulated sugar into a small saucepan. Cook over medium heat, whisking continuously until the mixture starts to boil.
Remove from heat and whisk in 1 Tbsp cocoa powder. Pour into a small bowl to cool to room temperature, then cover and set aside. If you're making this in advance, it can be stored in an airtight container in the fridge for up to 3 weeks.
Sift or whisk together 1 cup flour, 1 cup sugar, 1/3 cup dark cocoa powder, 1 tsp baking powder, 3/4 tsp baking soda, and 1/2 tsp salt in a large bowl. Set aside.
Into a separate, large bowl, add 1/2 cup warm water, 1/2 cup sour cream, 1/4 cup oil, 1 egg, 1 tsp vanilla, and 1 tsp instant espresso (optional). Whisk together until combined.
Add the dry ingredients to the wet ingredients and mix until just combined.
Pour the batter into the prepared pan. If desired, sprinkle 1/3 cup of chopped or mini chocolate chips on top of the batter. Bake for 28-32 minutes, or until a toothpick comes out with a few moist crumbs. Remove the pan from the oven.
Let the cake cool in the pan for 10 minutes, then carefully flip it onto a wire rack to finish cooling. If you're in a rush, place the whole pan in the freezer for 30 minutes to accelerate the cooling process.
Chocolate Buttercream
While the cake bakes and cools, make the chocolate buttercream. Start by melting 1/4 cup of dark or milk chocolate with either a microwave or double boiler. Set aside to cool.
In a large glass bowl or the bowl of a stand mixer, beat 1/2 cup of room-temperature butter on a medium speed for 30 seconds with a hand mixer or paddle attachment until smooth.
Mix in 1/4 cup cocoa powder, 1 tsp vanilla extract, and 1/4 tsp salt on a low speed.
Slowly mix in 1 1/2 cups of powdered sugar and 1/4 cup of heavy cream on a low speed. Once combined, mix in 1/4 cup of melted and cooled chocolate. The chocolate should still be fluid, but it shouldn't be hot to the touch.
Mix on low until the ingredients are fully incorporated and the desired consistency is reached. If the frosting seems too thick, add extra heavy cream one tablespoon at a time. If it's too thin, add in additional powdered sugar 1/4 cup at a time.
Once the ingredients are combined, stir by hand with a rubber spatula for a couple of minutes to make the frosting super smooth. Cover flush with plastic wrap and set aside.
Decorating This Chocolate Snack Cake
If you made the chocolate simple syrup, use a fork to poke holes in the top of the cake. I like to space the holes about an inch apart. Use a silicone brush or kitchen brush to brush the cake with chocolate simple syrup to make it extra moist.
Use an offset spatula or the back of a spoon to spread the chocolate buttercream on top of the fully cooled snack cake.
The ganache should have thickened by this point and be scoopable. If you made it in advance and it's chilled, set the container out a few hours ahead of time to let it come to room temperature before using it. You can also heat it in 10-second intervals in the microwave at half power, stirring between intervals until it softens and can be scooped.
Swirl the chocolate ganache into the chocolate buttercream, and top with a sprinkle of flakey sea salt and chocolate shavings (I use a chocolate bar and a vegetable peeler to make them). Then enjoy!
Video
Notes
Ingredient Swaps & Substitutions
For a detailed list of ingredient swaps and substitutions that can be made in each component of this recipe, please refer to the "swaps and substitutions" section above.
Making This Chocolate Snack Cake in Different Sizes
This recipe can be made in a round or square 8-inch pan. Bake time will be a couple of minutes longer in a round pan than in a square pan.This recipe can also be used to make two, 6-inch cake layers with one batch of batter. Bake at 350 F / 175 C for 30-33 minutes, or until a toothpick inserted in the center of the layer comes out with a few moist crumbs.You can also make one, 9-inch cake layer. Bake at 350 F / 175 C for 30-35 minutes, or until a toothpick inserted in the center of the layer comes out with a few moist crumbs.If you want to make a loaf cake using this recipe, use an 8.5x4.5-inch pan and bake for 50-60 minutes at 350 F / 175 C.
Tips for Making the Chocolate Snack Cake
Ingredients at room temp mix together better. Set out any cold ingredients ahead of time.
Properly measure the flour (spoon into the cup measure, then level) or use a kitchen scale to measure your dry ingredients.
Mix the cake batter just until the ingredients are incorporated once you add the dry ingredients. This will ensure your cake bakes up tender and soft.
Make sure the cake is fully cooled before you frost it. Otherwise, the frosting will melt right off the cake!
Give the chocolate ganache time to cool to room temperature. This will give it a thicker consistency and make it easier to swirl into the frosting.
Chocolate Snack Cake Variations
To make a gluten-free chocolate snack cake, swap in your favorite gluten-free flour blend for the AP flour this recipe calls for. Be sure to over-mix the batter and let it sit for at least 30 minutes before baking for best results.
Making This Chocolate Snack Cake in Advance & Storage Tips
You can make this cake in advance! A frosted cake can sit at room temperature for up to 2 days or be stored in the fridge for up to 5 days in an airtight container.It can also last up to a month in the freezer. If you plan to freeze it, I suggest waiting to frost it until it's thawed.The ganache can also be made up to a month in advance. Store it in the fridge in an airtight container for up to a month. When you're ready to use it, heat it in 10-second intervals until it reaches a spreadable consistency.You can also make the buttercream ahead of time or save any leftovers. This buttercream frosting will last in the fridge for up to a month.Be sure to give the frosting a good stir once it thaws to get the consistency nice and smooth again.