5-Ingredient Fix Contest Entry. This is an incredibly moist cake, thanks to the mashed potatoes in it! And with so few ingredients, it's super easy to make. Like any cake recipe, it can be made as a layer cake, bundt cake, cupcakes, or in a 9x13-inch pan, as this recipe describes. And since it calls for a cake mix, you can make it in a variety of flavors. I came up with this idea after growing up on Spud Nuts - those amazing donuts with potatoes in them, so I figured potatoes would make cakes better, too. And they do!