Rinse the mussels in plenty of cold running water before scraping them clean and removing their beards. Rinse them again and set aside.
Rinse the rice in several changes of cold water. Bring a pot of well-salted water to the boil and add the rice, cooking it for 9 minutes. Drain the rice and keep warm.
Meanwhile, heat a large saucepan, flameproof casserole dish or wok with the o