5-Ingredient Fix Contest Entry.As beautiful to look at as it is delicious, this 'gateau' is a dynamite way to use leftover mashed potatoes! I have made a mushroom version for years using simple crepes, but I think the potato crepes and prepared creamed spinach re-work is even yummier, and a presentation that will bring raves. Upgrade a simple roast or chicken to company fare with this recipe, serve by itself with a salad as a lighter meal, or pair with eggs for a really special brunch. Note: You can even prepare the batter ahead and let it rest overnight in the refrigerator. Bring to room temp and stir well before using, if you do. Or even, make the potato crepes ahead and refrigerate or freeze with sheets of waxed-paper between them. Thaw and bring to room temp to use though!