I decided to do this recipe after finding the remaining sweet potatoes from a pack I'd bought a couple of weeks ago. After assembling the gratin and putting it in the oven, I found one lonely sweet potato on the kitchen floor. It must have fallen out of the bag without me noticing. So I still have one sweet potato which needs eating.
Take two sweet potatoes and two small onions. Slice them and fry for a few minutes. Add some stock and boil until all the stock has evaporated and the slices have started to soften. Grate 100g of cheese.
Meanwhile a small amount of thick cheese sauce, using flour to thicken the milk and a small amount of the grated cheese.
Put half of the slices in the bottom of an oven proof bowl. Sprinkle half of the cheese and then add the rest of the slices. Pour over the cheese sauce and top with the remaining cheese.
Cook at gas mark 6 for 25 minutes until the cheese has melted and the sauce is bubbling. Serves 2 as a side dish.