It’s an ingredient forgiving of an empty cupboard, can be treated in myriad ways, is relatively easy to cook and is utterly sustainable. Perfect!
Before mussels can be cooked, they must first be chosen. The process is a bit like selecting jurors for trial: you start with a random pool assembled by someone else, and eliminate any that are obviously disqualified – the broken, the dead. Some you can interrogate a little: tap any open mussels sharply against the side of the sink, and if they close up in response, they’re OK. One or two may be subject to peremptory challenge – you’re allowed to get rid of them without giving reasons, just because you don’t like the look of them. It’s not hard, but there’s a level of responsibility involved.
You also need to tug off their beards – generally a bit of whatever it is they were clinging on to when they were harvested, in most cases the rope they were grown on. Sometimes, they need a bit of scrubbing, but the mussels sold in nets on the supermarket fish counter are pretty clean – they’ve already been subjected to a level of abrading on your behalf. You can scrape off any remaining barnacles with the blunt edge of a butter knife, but honestly, unless you’re planning to photograph your dinner, I wouldn’t bother.