Mussels don't have the reputation of their more expensive cousins, clams and oysters. Like these, they're officially called univalve mollusks but, unlike them, mussels are almost always cooked. So they come to mind as the weather cools, since they're perfect for warm, aromatic dishes.
Wild Mussels vs Farmed
Though it remains true that wild mussels taste better than farmed (wild oysters and clams are better than farmed, too, but you almost never see those), farmed mussels are better than they were, and they're a lot easier to clean -- they lack the "beard," the coarse vegetative growth that often extends from wild mussels' flat side -- so take what you can get. If your mussels do have beards, let them sit in a pot of cool running water for half hour or so, then scrub them, pull or cut off the beard, and rinse them. Discard any mussels with broken shells or open shells that don't close back up when you tap them, and also throw away unusually heavy mussels -- they're probably filled with mud.
Storing and Cooking Mussels
It's best to cook mussels soon after you buy them, but if you must store them, just keep them in a bowl in the refrigerator (not sealed, and not submerged in water). They'll stay alive for a few days.
You can broil mussels, or grill, roast, sauté, deep-fry, shuck and boil (in soup), or split and bake them, but steaming is the easiest and most common way to cook them. It's also, frankly, the best, because it leaves you with a mouthwateringly delicious broth that you can serve along with the mussels. If you use a steaming liquid other than water -- say, beer, wine, stock, or even canned tomatoes -- and if you add aromatic vegetables and other flavoring agents to the pot, the broth becomes even more spectacular.
The only caveat when it comes to steaming mussels is that they will certainly release some sand into the pot as they open. There's no way around this: Even if you scrub them well (and you should), they'll still contain a little sand inside their shells. So after you steam them, remove them and whatever other ingredients you want to eat from the pot with a slotted spoon, and then slowly and carefully pour the liquid over the mussels, leaving a few tablespoons in the bottom of the pot to trap the grit.
One of my surefire recipes for steamed mussels is based loosely on how they're served in Belgium: steamed in beer seasoned with shallot, leek, garlic and fennel. There are probably about a million equally authentic variations of Belgian-style mussels -- some with butter, some with cream, some with herbs -- but this one does it for me: The subtle fragrance of the leeks and shallot, the gentle anise aroma of the fennel, and the briny flavor of the mussels go beautifully together. You can use any beer to cook mussels in -- I suppose a Belgian-style beer is most appropriate-but in any case, drink some of the same beer as you eat. If you want a truly Belgian experience, serve the mussels alongside French fries-and, in any case, be sure to have plenty of good crusty bread on hand to sop up the broth.
Mussels Over Pasta
Alternatively, you can serve mussels with pasta -- the pasta soaks in the mussels' juices and any other flavors you care to add to them. Though this preparation obviously originated in Italy, my favorite way to do it has a Portuguese accent in the form of smoked sausage. Tomatoes, garlic, and basil combine to form a typical red sauce that is enlivened by the assertive mussels and smoky sausage.