3Heat the olive oil in a Dutch oven over medium-high heat on a grate over a grill or on the floor of a wood-fired oven. Add the onion, celery, and carrots and sauté for 5 minutes. Add the garlic and sauté for 2 minutes. Remove the shells from the warm broth and add three-quarters of the liquid to the sautéed vegetables. Add the wine, salt, pepper, saffron, thyme, and bay leaves; bring to a boil. Move to a cooler area of the oven and simmer for 15 minutes; discard the bay leaves. Return to a boil, add the fish, and simmer for 5 minutes. Add the remaining stock, the scallops, and mussels and cook for 2 minutes. Add the shrimp and cook for another 3 minutes. Taste and adjust the seasoning. Bring to a low boil for 1 minute.