Sometimes I use 8 ounces of sour cream for the topping and sometimes I use 16 ounces. It depends how thick you want your topping to be.
This recipe is 1½ times what Hershey's Chocolate Cake recipe calls for, which makes it easier to frost the cake. Also, make sure the cake is thoroughly cool before trying to frost it because it is a very moist cake.
I mix my dry ingredients in the same bowl as the butter to make one less bowl to clean.