1. Cut the base of the fennel and the tip of the stems. Cut the bulbs into quarters, rinse and slice.

2. Peel and finely chop the onion.

3. In abundant salted boiling water, blanch the fennel for 5 minutes; drain and let cool.

4. Preheat the oven to 200°C.

5. Remove the seeds from the pumpkin with a spoon. Peel and cut the flesh into 1 cm thick slices.

6. Butter a gratin dish. Layer a layer of pumpkin, sprinkle with onion and fennel; repeat until finishing with a layer of onion and fennel.

7. In a saucepan, heat the milk and cream. Season generously with salt and pepper. Bring to a boil. Pour this mixture into the gratin dish.

8. Sprinkle with grated Gruyère and the remaining butter in small pieces.

9. Bake and cook for 30 minutes.

10. Remove from the oven and serve immediately.