FOUR-LAYER CHOCOLATE CAKE

Steps:

• Preheat the oven to 350 degrees F. Spray two 8-inch cake pans with nonstick cooking spray and line the bottoms with parchment. Spray the parchment and dust with flour.
• Whisk together the flour, cocoa, baking soda and salt in a large bowl.
• Beat together the butter and sugar in a stand mixer until light and fluffy, 1 to 2 minutes. Add the eggs one at time and beat until incorporated. Add the sour cream and continue to beat until fully incorporated. Then add the vanilla.
• Stir together the instant espresso powder with the hot water in a spouted measuring cup. With the mixer running, add the dry ingredients in two additions, alternating with the espresso.
• Divide the batter between the cake pans and bake until a tester inserted in the centers comes out clean, 30 to 35 minutes. Cool the cakes in the pans on a rack for 10 minutes, then remove the cakes to the rack to cool completely.
• Slice a thin layer from the top of each cooled cake with a serrated knife to remove the domed top. With a serrated knife, slice the layers in half horizontally to make 4 layers. Spread buttercream on the cut side of a layer and sandwich another layer on top. Repeat with the remaining frosting and layers, leaving the last top layer unfrosted.
• Apply a thin crumb-coat of frosting to the entire cake and chill in the refrigerator at least 15 minutes to set. Use the remaining frosting to generously frost the cake.
• Put the egg whites and sugar into a large bowl set over a double boiler. Whisk constantly until the sugar melts and the mixture is very thin and warm.
• Pour the egg whites into the bowl of a stand mixer fitted with the whisk attachment and whisk on high speed until stiff peaks form, about 5 minutes. Turn to low speed and continue beating until cool, about 10 minutes.
• Turn the mixer to medium speed and whisk in the butter in small pieces. (The mixture may look curdled before it comes together.) Add the vanilla extract. Re-beat the mixture as needed to keep it smooth as you frost your cake.