Combine the cream and powdered sugar in the bowl of a stand mixer fitted with a whisk attachment.
Whip the cream on medium-high speed until firm peaks form.
You can use a knife to spread the whipped cream between each layer of cookie, but if you have a piping bag, I recommend putting the cream in a piping bag fitted with a round tip–it’s faster and neater. Either way, spread a thin layer of cream on the bottom of a cookie, and place the cookie onto a plate, cardboard round, or other serving surface. After the cakes are assembled the cookies will soften into a cakey texture, so it’s difficult to transfer them later. I put mine on doily-covered cardboard rounds, so they were easy to serve individually.
Pipe or spread a thin, even layer of whipped cream on top of the cookie.
Top the first cookie with a second, and continue to layer cream and cookies until you have a stack of six cookies. (You can play with the height–I found that six cookies made a nice, tall cake that seemed substantial but wasn’t too overwhelming. You can find what height works for you!)
Pipe or spread more whipped cream along the top and outside of the cake.
Use an offset spatula or a knife to spread it into a smooth layer. The cake might shift around while you’re working on it, since whipped cream is delicate, so be gentle! Don’t worry about having a perfect finish, because you can always cover up any trouble spots with candy later on.
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.
Now for the fun part! Decorate the cakes with an assortment of Valentine’s Day candy, and additional whipped cream, if desired. Depending on the candy you choose, the coloring might start to seep into the whipped cream as it sits, so that’s why it’s best to decorate these shortly before you plan on serving them.