Special equipment: three 8-inch round cake pans and a candy thermometer
For the cake: Preheat the oven to 325 degrees F. Butter three 8-inch round cake pans and dust them with cocoa powder.
With an electric mixer, cream together the butter and sugar. Add in the eggs one by one until incorporated. Add the buttermilk and vanilla. Sift together the cocoa powder, flour, baking powder, salt and baking soda. Stir the dry mixture into the wet mixture until incorporated.
Divide the batter equally among the prepared pans and bake until a toothpick inserted in the center of the cakes comes out clean, about 30 minutes. Cool the cakes on a rack for 10 minutes, then remove them from the pans and cool completely on the rack.
For the vanilla Italian buttercream: With an electric mixer, beat the egg whites and 3/4 cup of the sugar to stiff peaks. Heat the remaining sugar and 1 1/4 cups water to 240 degrees F in a small saucepan over medium-high heat. Pour the boiling syrup into the egg whites, and beat until cooled to room temperature, 8 to 10 minutes. Cube the butter and add it to the bowl slowly. Mix until fluffy. Beat in the vanilla until incorporated.
To assemble the cake, coat the top of 1 cake round with some of the buttercream. Stack the next cake round and coat with some buttercream; repeat until you have 3 layers. Then frost the sides with the remaining buttercream.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.