I came up with this for a Mardi Gras themed birthday party. It's a super moist sour cream banana cake adapted from an Elisa Strauss recipe, with pastry cream filling, rum buttercream, and caramel sauce. You can certainly use a store bought caramel sauce, but this is incredibly better and easy to make if you're patient. I know it's an effort to make this cake, but it is a real showstopper. If you really like to bake, then it's worth every minute! Make ahead: Cake - 2 days refrigerated, 1 month frozen; Pastry Cream - 1 day refrigerated; Buttercream - 1 week refrigerated, 1 month frozen; Caramel - 1 week refrigerated