Clean mussels and remove the beards by giving a sideways chuck – a downwards one will tear the mussel. Remove any barnacles also as they will fall off and ruin the sauce. NB: Discard any open mussels.
Cook the onion in a little oil until, soft. Add the wine and the mussels, cover and shake occasionally until the mussels are open. Now add some pepper from the mill, then the cream. Bring to the boil, shaking again, and transfer to a tureen.
Sprinkle with parsley and serve immediately. NB: It is very important to discard any unopened mussels – do not overcook in an attempt to open them.