Gracias Candice e Aurélie.
Ingredients for 4 persons:
1 kg Potatoes (yellow flesh variety)
1 garlic clove
Take some yellow flesh potatoes (Holland variety for example), peel them and cut them into thin slices. Wash them and dry them properly.
Rub the inside of a dish with 1 garlic clove and then repeat this operation with the turnip. Place a layer of potato slices, season them with salt and pepper, add some nutmeg and cover with cream, then repeat this until you fill the dish.
Cook in the oven for 1 hour at 300°F (150°C or th.5), and then 30 min at 400°F (200°C or th.7) so that the top of the gratin becomes a golden brown.
You can add cheese on the top 10 or 15 minutes before the end if you want but you can also make it without cheese.