- Preheat the oven to 180°C (350°F).
- In a large pan heated to medium heat, pour in a drizzle of oil and cook the onions and the leaks until transparent. Add pepper, remove and set aside.
- Continue cooking until velvety.
- Pour half of the sauce into a buttered oven dish, spread half of the sweet potato strips over top, overlapping some of them.
- Add the diced ham, then the onion-leek mixture and pour in the rest of the sauce, keeping the surface smooth.
- Cover and cook for 45 minutes.
- Remove the lid, sprinkle on the grated cheese and continue cooking for 5 minutes or until nicely coloured.
- Serve hot.