Matelote Fish Stew

Name: Matelote (Fish Stew)
Ingredients: 14 to 16 ounces peeled or unpeeled pearl onions, fresh or frozen and thawed; Extra-virgin olive oil, for sautéing; 5 ounces pancetta, cut into lardons (about 1 cup); 8 ounces button mushrooms, halved; 1/4 cup cognac; 3 cups fish or seafood stock; 7 black peppercorns; 5 (2-inch) parsley stems; 3 thyme sprigs; 1 dried bay leaf; 1 garlic clove, peeled; 1 clove; Kosher salt, to taste; 1 (750-milliliter) bottle dry Riesling; 20 mussels, scrubbed and debearded; 8 ounces skin-on halibut (or monkfish), sliced into hearty chunks; 8 ounces skin-on sea bass (or perch), sliced into hearty chunks; 8 ounces Arctic char (or salmon), sliced into hearty chunks; 12 to 15 U/20 shrimp, peeled and deveined; 2 tablespoons all-purpose flour; 2 tablespoons unsalted butter, at room temperature; 3 tablespoons chopped flat-leaf parsley leaves; 1 tablespoon chopped tarragon leaves; Toasted baguette or sourdough, or cooked long noodles