Soak the mussels in plenty of cold water. Leave in the refrigerator until required. When ready
to use, scrub the mussel shells, removing any barnacles or beards. Discard any open mussels.
Melt the butter in a large pan. Add the mussels, onion and wine. Cover with a close-fitting lid
and steam for 5-6 minutes, shaking the pan gently to ensure even cooking. Discard any mussels that
have not opened, then strain and reserve the liquor.
To make the sauce, heat the oil in a medium-sized saucepan, and gently fry the quartered onion
and garlic for 3-4 minutes until soft and transparent. Stir in the tomatoes and half the reserved
mussel liquor. Bring to the boil and simmer for 7-10 minutes until the sauce begins to thicken.
Cook the pasta in boiling salted water for 7 minutes or or until al dente. Drain the pasta,
reserving 2 tablespoons of the cooking liquor, then return the pasta and liquor to the pan.
Remove the meat from half the mussel shells. Stir into the sauce along with the remaining
mussels. Pour the hot sauce over the cooked pasta and toss gently. Garnish with the parsley and