Cut the potatoes into thin slices (about 2-3 mm thick). Put them in a large bowl. Add salt, pepper and a little nutmeg. Pour over the cream and add 2/3 of the cheeses. Mix very well.

Place the slices vertically, in an ovenproof dish, approximately 20 x 30 cm. Place the chorizo slices between them. Pour the cream over them until it reaches about half way up of the potatoes (keep any left-over cream). Cover the dish with foil and bake at 200° C fan, for 45 minutes.Uncover and bake 15 minutes more.

Reduce oven to 180° C fan. Pour the remaining cream over the gratin and sprinkle with the remaining cheese. Bake 35-40 minutes until golden.

Let the potatoes stand for 15 minutes before serving.