Grease and flour two 9" round cake pans. Combine sugar, oil, water, eggs and cake mix in a large bowl. Add sour cream and mix thoroughly. Pour batter into the prepared cake pans. Back at 350 for 45-55 minutes, or until toothpick inserted in center comes out celan. Cool layers in pans on a wire rack for 5 minutes; remove from pans by inverting onto wire rack, and continue to cool.
Makes one double layer cake.
Cream butter well in a large bowl. Add cocoa and powdered sugar, mix at low speed and add milk. Beat until creamy. Place on cake layer on a plate and spread icing evenly over the top. Set the second layer on top of the first and spread icing on the sides and top of the cake.