Preheat the oven to 350 degrees F (175 degrees C).
Grease and flour two 9-inch round cake pans or one 9x13-inch dish.
Combine sugar, flour, cocoa, baking soda, baking powder, and salt in a large bowl. Make a well in the center. Pour coffee, buttermilk, oil, eggs, and vanilla into the well. Beat for 2 minutes on medium speed. Batter will be thin.
Pour into the prepared pans.
Bake in the preheated oven until a toothpick inserted into the center of the cake comes out clean, 30 to 40 minutes.
Cool for 10 minutes, then remove from the pans and finish cooling on a wire rack.
Fill and frost as desired.
