Easily prepare a tasty side dish that is quick to make. Practical and clever: while the gratin is quietly baking in the oven, you can sit comfortably on the couch for a quick check on social media or an episode of your favourite series.
Preheat the oven to Gas Mark 4, 180°C (350°F).
Wash, dry, peel and chop the potatoes and sweet potatoes.
Cook them in boiling water for 20 minutes. Check whether they are cooked with the tip of a knife.
Remove the potatoes from the water and drain well.
Place them in an ovenproof dish.
Mix the cream with a pinch of salt, a little pepper and the nutmeg. Pour this mixture over the potatoes and sweet potatoes. Add a knob of butter and the grated Gruyère cheese.
Bake for about 25 minutes.
Finish cooking under the grill for 5 minutes to brown the cheese.