I use with with my chocolate chiffon cake and its wonderful. With a white or yellow butter cake it should be just as great!

3 cups heavy cream
1-1/2 cups confectioners sugar
3/4 cup unsweetened cocoa
2 tsp vanilla
1/4 tsp salt

Whip very cold cream and all other ingredients till thick and holds its shape.

Frost sides and top (center too if 2 layer) with icing.
Its great!!!

If you are making a 9 x 13 you could use 2/3 of the recipe and have plenty.

Have fun!