Heat oven to 350°F. Grease and flour two 9-inch round baking pans or one 13x9x2-inch baking pan. Set aside. In the bowl of a stand mixer fitted with the whisk attachment or in a large bowl with an electric mixer, combine the sugar, flour, cocoa(s), baking soda, baking powder and salt. Mix on low until dry ingredients are thoroughly combined.
Add eggs, buttermilk, coffee, oil and vanilla. Beat on medium speed for about two minutes; the batter will be thin.
Pour batter evenly into prepared pans.
Bake in preheated oven for 30 to 35 minutes for round pans, 35 to 40 minutes for rectangular pan or until wooden toothpick inserted in center comes out clean.
Cool 10 minutes; remove from pans to wire racks. Cool completely.
Frost as desired. I used a simple and delicious Chocolate Buttercream Frosting from Savory Sweet Life. One batch was perfect for this chocolate layer cake.