1. Preheat the oven to 180°C (350°F).
2. Peel and slice the potatoes and pumpkin into thin slices.
Peel and slice the onions.
3. In a lightly oiled pan, sauté the onions, then add the liquid fresh cream, washed and dried basil leaves, salt, and pepper.
Mix well.
4. In a bowl, mix the slices of potatoes and pumpkin.
Arrange half of them in a buttered gratin dish, then pour the onion cream mixture over them, and cover with the remaining potatoes and pumpkin.
5. Bake for 20 minutes, add the grated cheese, then bake the dish for another 15 minutes.
6. Serve the Pumpkin and Potato Gratin when the cheese is golden brown.