Preheat the oven to 350 degrees. Grease and flour two 9-inch round cake pans. Or use baking spray with flour to generously coat each pan. Set aside.

In large bowl, whisk together sugar, all-purpose flour (sifted, spooned and leveled), cocoa powder, baking soda, baking powder, and salt.

Add eggs, milk, oil, and vanilla; mix for 3 minutes with an electric mixer. Stir in boiling water by hand. Pour evenly into the prepared pans.

Bake 30 to 35 minutes in preheated oven. Cakes are done when a toothpick inserted into center comes out clean. Cool 30 minutes before removing from pans (this step is important). After removing from pan, place cooled cakes on wire racks to cool completely.

While cakes cool, make frosting. Use an electric mixer to cream butter until light and fluffy. Stir in confectioners' sugar and cocoa alternately with milk and vanilla. Beat until light and smooth.

2-LAYERS: Use a serrated knife to cut away peaks on top of each layer. Make sure top of cake is smooth. Stack on serving plate. Spread frosting over top of each layer.

4-LAYERS: Use a serrated knife to cut away peaks on top of each layer. Make sure top of cake is smooth. Use a serrated knife to split each cooled cake layer horizontally. Spread frosting over top of each layer. Stack each layer on serving plate.

Frost outside of cake with remaining frosting.

GARNISH: Sprinkle top of frosted cake with cocoa powder or garnish with shaved chocolate. Both are optional.

Makes one 9-inch cake (2 layers or four layers).