Brindisi Seafood Stew

Name: Brindisi Seafood Stew
Ingredients: ½ cup extra-virgin olive oil, plus more; 1 celery stalk, coarsely chopped; 1 garlic clove, finely chopped; 1 yellow onion, coarsely chopped; Crushed red chile flakes (optional); 14 oz. cuttlefish, cleaned and cut into ½-in. pieces; 14 oz. squid, cleaned and cut into ½-in. pieces; Kosher salt; 2 medium tomatoes, coarsely chopped; 2½ lb. firm white fish, such as rockfish, cleaned and cut into 2-in. pieces; 1 lb. hard clams, scrubbed; 1 lb. mussels, scrubbed and debearded; 10 medium shrimp; 4 large prawns; Finely chopped parsley leaves, for garnish; Toasted crusty bread, for serving