Peel the potatoes and cut into 3 cm cubes. Wash the leek and cut into 1 cm wide rings.
Heat the butter in a saucepan. Add the potatoes and leek and sweat until the leek begins to turn translucent. Now add the broth and simmer for 15 minutes.
Thicken the cooking stock with a little cornstarch and bring it to the boil again. Add the cream and season with salt, pepper and nutmeg.