Preheat oven to 350 degrees F (175 degrees C). Lightly grease and flour three 9 inch round cake pans.

Place the sugar and butter in a mixing bowl, and beat until light colored and smooth. Beat in the eggs one at a time. Stir the coffee and cocoa into the egg mixture until well blended. Measure the buttermilk, and remove 1 tablespoon, placing it in a separate small bowl, and set aside. Stir the remaining buttermilk into the egg mixture, beating until smooth.

Stir the baking soda into 1 tablespoon buttermilk until smooth, and mix into the egg mixture. Stir in the flour, beating until smooth. Pour the batter evenly into the prepared cake pans.

Bake in preheated oven until a toothpick or small knife inserted into the center comes out clean, about 30 minutes. Remove from the oven, and cool in the pans about 15 minutes before turning out onto a wire rack to cool completely.

To make the frosting, beat 1 cup butter until smooth and creamy. Gradually sift in the confectioners' sugar, and beat until smooth. Stir in the coffee, cocoa, and vanilla until well blended.

Place one cake layer on a serving plate. Spread top with about 1/5 frosting. Place the second layer on top of the first, and frost. Repeat with the third layer. Use remaining frosting to frost top and sides.