Put the mussels in a saucepan with just under 1 quart of water, 1 chopped onion, and 1 or 2 bayleaves. Cover and cook for a few minutes, till the shells are opened, then pour the liquid into a basin through a sieve. Remove the mussels from their shells and put them on a plate. Put 2 or 3 tablespoons of oil in a saucepan and, when hot, add the leek, finely chopped, and cook till brown. Add the water in which the mussels were cooked, add the rice, the saffron, and simmer till the rice is tender. The mussels are added a few minutes before serving. A chopped tomato is sometimes added, and often vermicelli is used instead of rice.