Black Sea Bass and Mussels a la Nage

Name: Black Sea Bass and Mussels a la Nage
Ingredients: Kosher salt; 3/4 cup fresh fava beans; 1 cup sliced-on-the-diagonal asparagus; 1/2 shelled peas; 1 teaspoon plus 4 tablespoons unsalted butter; 2 tablespoons minced shallot; 4 (6-ounce) skin-on black sea bass fillets (snapper or sole may also be used); Freshly ground black pepper; 24 mussels, washed and de-bearded; 3/4 cup dry white vermouth; 1/2 cup water; 1 sprig fresh tarragon, leaves picked and chopped; 1 teaspoon finely sliced fresh chives; 1 teaspoon finely chopped fresh flat-leaf parsley leaves; 1/2 teaspoon finely chopped fresh dill