People might think that this is too fiddly and bothersome to be attempting at home, when in fact it's easypeasy - 5 minutes with a sink and the cold water tap and the mussel shells are cleaned and ready. Then it's the simplest of recipes.
As regards food safety, this quote is from the BBC. You trust them, don't you?
"Unless you know how fresh they are, always eat mussels on the same day you buy them. Carefully place the blue-black mussels into a sinkful of cold water and discard any that stay open when tapped. Pull away their beards and, if you are presenting them in their shells, it's a good idea to give them a good scrub, scraping off any barnacles. A final couple of rinses will ensure a sand-free meal...[when cooking] as soon as the shells start gaping open, you know they are ready. Don't overcook them or you'll end up with rubbery flesh. Discard any that fail to open fully."
1 medium onion, finely chopped
2 garlic cloves, finely chopped
a handful of parsley, chopped
150ml dry white wine
1kg mussels, scrubbed; any open ones discarded.
30g butter, cubed
salt + black pepper
chopped flat-leaf parsley to serve
Simmer the onion, garlic, parsley and wine for about 5 minutes. Add the mussels, increase the heat and cover. Check after 2 minutes or so - remove any unopened mussels. Strain the liquor into a small pan, whisk in the butter and season. Put the mussels into bowls, pour over the liquor and sprinkle with more parsley.