In a large saucepan with a lid, over medium heat, melt half the butter.
3 tablespoons unsalted butter
Add shallots, leek, garlic, and bay leaves.
3 tablespoons sliced leek, 2 tablespoons sliced shallot, 1 tablespoon sliced garlic, 2 bay leaves
Stir occasionally until vegetables are soft but not brown (about 6 minutes).
Season with salt and freshly cracked pepper.
¼ teaspoon kosher salt, ½ teaspoon freshly ground black pepper
Crank up heat to high and add white wine.
1 cup dry white wine
When the wine has reduced by about half, add mussels, give it a good stir, and put the lid on.
2 pounds fresh mussels, cleaned
Shake the whole pan with a lid on, several times per minute. After a few minutes, check if the mussels have opened. It will only take three to five minutes.
As soon as they’re open, transfer to a warm bowl and cover with a lid or foil to keep mussels warm.
Remove pan from heat, add remaining butter and crème fraîche, and whisk until it has emulsified. Taste the sauce you just created and season to your liking.
3 tablespoons unsalted butter, 3 tablespoons crème fraîche (or heavy cream)
Put the mussels back into the pot.
Add lemon zest, lemon juice, and parsley, and stir.
1 tablespoon lemon juice, 1 teaspoon lemon zest, 4 tablespoons minced fresh parsley leaves
Serve immediately on warm plates with toasted baguette. Don’t forget to spoon over all the remaining sauce in the pot!
French baguette (optional)