Heat the oil in a large saucepan, add the fennel, leeks and garlic and cook over a low heat for 5 minutes until the leeks wilt. Add the wine and stock, remove from the heat and set aside.
Meanwhile, scrub the mussels if necessary, scraping off any barnacles and pulling away the beards. Discard any with damaged shells, and any that do not close when tapped sharply on the edge of the sink.
Bring the wine and vegetable mixture to the boil, then add the mussels. Cook, covered, over a high heat for 3-4 minutes, shaking the pan from time to time, until the shells open.
Using a slotted spoon, remove the opened mussels to a bowl, discarding any that have not opened.
Pick the mussels from the shells, leaving some in for decoration, if desired, and return them to the broth. Heat gently, whisk in the cream and add black pepper to taste. Transfer to warmed bowls, sprinkle with parsley and serve with homemade soda bread.