You Will Need:
4 pounds mussels, scrubbed, debearded
1 fennel bulb, trimmed, cut into 1″ cubes or thinly sliced
1 cup verjus (or 1/4 cup apple cider vinegar and 3/4 cup white grape juice)
1/3 cup dry white wine
1/4 cup (1/2 stick) unsalted butter, cut into 1/2″ pieces
1 cup lovage leaves or celery leaves, divided
Kosher salt and freshly ground black pepper
Heat a large heavy pot over high heat until very hot. Add mussels, fennel, verjus, and wine. Cover and cook, stirring frequently, until mussels fully open (discard any that do not open). Using a slotted spoon, transfer mussels and fennel to a serving platter.
Simmer liquid in pot for 1 minute; whisk in butter and 1/2 cup lovage leaves. Season to taste with salt and pepper (and additional vinegar if using grape juice). Spoon over mussels, leaving any sediment behind. Garnish mussels with remaining 1/2 cup lovage leaves and serve immediately.
See Recipe in epicurious.com