Spread more whipped cream along the outside of the cakes, and smooth it into an even layer. Don’t worry about being too precise, since you can use the candy to cover up any big mistakes. After all of the cakes are assembled, refrigerate the cakes for at least 3 hours, to give the cookies time to soften. The cakes can be made several days in advance and kept, refrigerated, until you’re ready to decorate them.