In a mixer bowl, mix the dry cake mix with the eggs, water, and oil. Blend until creamy 2 minutes and pour into 2 9'inch round parchment lined pans.
Bake the layers at 350 for 35 minutes or until cakes spring back in middle or tests done in center with a toothpick. Remove and cool completely, then remove parchment from bottom.
Chocolate Buttercream- In a mixer add butter with powdered sugar, cocoa, and add vanilla to half and half or milk a little at a time on lowest speed until frosting is creamy. You may need to add a little more milk to get the right consistency. It should look creamy but not runny.
With parchments removed, place first layer face down frost top of layer then add second layer face up. Frost sides then top of cake and set 2-3 hours to let the frosting firm up before serving.