Rustic Cioppino with Aioli

Name: Rustic Cioppino with Aioli
Ingredients: 8 Tbs. (1 stick) (4 oz./120 g) unsalted butter; 1 yellow onion, diced; 1 small fennel bulb, trimmed and thinly sliced; 6 garlic cloves, thinly sliced; Kosher salt and freshly ground black pepper; 1 Tbs. tomato paste; 3/4 cup (6 fl. oz./180 ml) dry white wine; 1 can (28 oz./875 g) diced tomatoes; 1 bay leaf; 1/4 tsp. red pepper flakes; 1/2 lb. (250 g) clams, scrubbed; 1/2 lb. (250 g) mussels, scrubbed and debearded; 1/4 lb. (125 g) shrimp, peeled and deveined, tails intact; 2 fresh oregano sprigs; 2 fresh flat-leaf parsley sprigs; 1 fresh tarragon sprig