Pre-Heat oven to 350°F. Grease and flour three 6-inch round baking pans.Add eggs, oil and vanilla to a stand mixer. Beat on medium speed for 2 minutes.Add in dry ingredients. Mix again. While the stand mixer is going, add in the buttermilk. Stir in boiling water or coffee. Divide batter equally between the prepared pans.Bake 40-45 minutes. Cool on a wire rack.
Frosting
Add butter and cocoa to a stand mixer. Alternately add powdered sugar and heavy cream, beating to spreading consistency.Add small amount additional heavy cream, if needed. Stir in vanilla. Frost the bottom layer. Add the second layer and frost the whole cake.