1. Wash and peel the potatoes, and cook them in a large pot of salted water.
2. Warm the duck legs in a double boiler to remove them from their fat.
3. Reserve one tablespoon of duck fat.
4. Cut and roughly chop the confit duck legs (do not use a blender!).
5. Slice the shallots and onions.
6. In a large skillet or sauté pan, sauté the chopped onions and shallots in the tablespoon of duck fat over low heat.
7. When the onion and shallot mixture is golden brown, add the chopped duck and cook over high heat, stirring vigorously, for 5 minutes. The duck should be finely browned on the surface but remain tender. Remove from heat and set aside.
8. Mash the potatoes with a fork (please, no potato masher!) and make a creamy mash by adding 50% water and 50% milk.
9. Season with salt, pepper, a pinch of nutmeg, and the cream.
10. Preheat the oven to 200°C (400°F).
11. In a deep dish, spread half of the duck mixture.
12. Mix the remaining half with the same amount of mashed potatoes, and spread this second layer over the first. Finish with a third layer of mashed potatoes.
13. Score the top of the mashed potatoes with the back of a fork.
14. Bake in a hot oven (200°C/400°F) for 25 minutes. You can also finish cooking for 3 minutes under the broiler to achieve a nice gratin.
15. Serve with a salad (such as lamb's lettuce) and a light Cahors wine: this dish may not look fancy, but your guests will be pleasantly surprised!