- Preheat the oven to 190C/Gas Mark 5 and butter a large gratin dish. And sweet potato slices, chestnuts, garlic, oil, half the cream, rosemary, chilli if required, and salt and pepper to a large mixing bowl and toss until coated.
- Layer the slices/mixture in the butter dish and build up until full. Pour over the remaining cream.
- Cover the dish with foil and bake for approx. 35 mins. Take off the foil, sprinkle with grated cheese and bake uncovered for a further 30 minutes until crisp and brown. 7. Serve immediately.