1. Mix the softened butter, sugar, eggs, and sour cream together in a large bowl. Set aside.

2. In a sifter, add the flour, baking powder, soda and salt, and sift gradually into the butter mixture. Blend well. Add the vanilla.

3. Pour half the cake batter in a greased 13 x 9 x 2 pan. Sprinkle with half of the topping mixture, and add the remaining cake mixture. Sprinkle with the remaining topping mixture. If you wish, you may swirl the topping mixture into the cake mixture.

4. Bake at 350F for 35 minutes or until the cake springs back.

Topping: To prepare, mix all ingredients together.

Icing: Mix all ingredients together in a bowl and set aside. While the cake is still warm, pour on top of cake.