Melt butter over medium high heat in a small stock pot, taking care to not let the butter brown. Once butter has melted, stir in the sliced onions and sauté until they are soft and translucent.
Once the onions have cooked, stir in the garlic and the herbs, and cook for about a minute. Don't let the garlic burn. You could technically tie the herbs together in a bouquet garni, but I live leaving them loose because I like the rustic look and the way that you are more likely to get a bit of rosemary or thyme in a bite if you don't. Do whatever makes you happy.
Add the wine and let it cook down for about a minute.
Add the mussels and cover for about two-to-three minutes.
Stir to ensure that the mussels have all been steamed. When mussels are properly steamed, they open.
Discard any mussels that did not open after cooking.
Taste the pot liquor/broth and then add salt, pepper lemon zest, and/or Old Bay, to taste.
Serve the mussels on soup plates or shallow bowls with plenty of pot liquor, and a generous portion of french fries and french bread on the side. Some people may want to lightly toast their bread first, but I will eat it either way as long as I can dip lots of it asap.
If you happen to have any mussels left over, I suggest taking them out of the shell and storing them with a generous portion of the pot liquor poured over it. You can reheat it over medium heat the next day.
