Remove the outer leek leaves and cut the leek in half longwise. Wash well and cut into about 2cm wide slices. Heat 2 tablespoons of butter in a saucepan and sauté leeks in it briefly.
Add the stock to the saucepan and simmer for 5-6 minutes then add the rice and cook everything without covering or stirring for 18-20 minutes until the rice is tender and all the stock has been absorbed.
Melt the rest of the butter but don't let it go brown then mix with the grated cheese. Just before serving mix the cheese with the leek. Season with the pepper and nutmeg.