Instructions:
- Prepare the Cake Pans: Preheat your oven to 350°F (175°C). Butter two 9-inch round cake pans, then line the bottom of each pan with a round of parchment paper. Butter the parchment paper as well. If you want more level cakes, you can use cake strips that have been soaked and fully saturated with water (see notes below), or you can level the tops after baking.
- Mix the Dry Ingredients: In a large heat-proof mixing bowl, whisk together the 1 1/2 cups granulated sugar, 1/2 cup brown sugar, 3/4 cup unsweetened cocoa powder, 1 teaspoon baking soda, and 3/4 teaspoon salt. Once mixed, carefully pour in the boiling water, whisking immediately to combine. Allow the mixture to cool for about 5 minutes.
- Add Wet Ingredients: Using an electric hand mixer on low speed, blend in 3/4 cup vegetable oil and 1/4 cup melted butter until the mixture is well combined. Add the 2 eggs, 3 egg yolks, and 1 tablespoon vanilla extract, then beat just until everything is fully combined. Be careful not to overmix.
- Add the Dry Ingredients: Gradually add the 2 cups all-purpose flour to the wet mixture, blending just until combined. Then, mix in the 1/3 cup milk and 1/2 cup sour cream until smooth.
- Prepare to Bake: Divide the batter evenly between the two prepared pans. Use a spatula to smooth the tops of the batter. Bake in the preheated oven for 29-34 minutes, or until a toothpick inserted into the center of the cakes comes out clean or with a few moist crumbs.
- Cool the Cakes: Once baked, allow the cakes to cool in the pans for 5 minutes. Then, run a butter knife around the edges of the pans and invert the cakes onto a wire rack. Remove the parchment paper and let the cakes cool completely.
- Trim the Cakes: If necessary, trim the tops of the cakes to make them level. You can do this using a serrated knife to carefully slice off any domed tops, creating an even surface for frosting.
- Prepare the Frosting: In a medium-sized mixing bowl, beat the 1 cup softened butter until smooth and creamy. Add the 3 1/2 cups powdered sugar and 1/2 cup unsweetened cocoa powder, mixing well until smooth. Add 1/4 cup heavy cream, 1 teaspoon vanilla extract, and a pinch of salt, and continue beating until the frosting is light and fluffy. You can adjust the consistency by adding more cream if needed.
- Assemble the Cake: Place one cake layer on a serving platter. Spread a generous layer of frosting over the top. Place the second cake layer on top, then frost the top and sides of the cake with the remaining frosting. Smooth the frosting with a spatula for a clean finish.
- Serve: Allow the cake to set for a few minutes before slicing and serving. Enjoy the rich, chocolatey goodness of this homemade chocolate cake with chocolate buttercream frosting!
Notes:
