Combine all ingredients except frosting in a large mixing bowl; beat 4 minutes at medium speed with an ele4ctric mixer. POur batter into 2 greased and floured 9 inch round cake pans. Bake at 325F for 35 minutes or until a wooden pick comes out clean. Cool in pans 10 minutes; remove from pans, let cool on wire racks.
Spread Sour Cream Chocolate frosting between layers and on top and sides of cake.
Sour Cream Chocolate Frosting: Place chocolate in top of a double boiler; bring water to a boil. reduce heat to low; cook until chocolate melts. Cool.
Combine chocolate and sour cream. Add sugar alternately with milk,bating at med. speed until smooth.