For the Shrimp Stock:
2 In a small saucepan, combine the shrimp shells, carrot, celery, onion, garlic, parsley, bay leaves, salt and pepper. Add 1.5 quarts filtered water or enough to cover the ingredients in the pot. Set over high heat and bring the liquid to a simmer, lower the heat to medium-low, cover partially with a lid and cook until the liquid has reduced in volume by ¼, 12 to 15 minutes. Taste for seasoning and adjust with salt and pepper as desired.
3 Pass the stock through a sieve into a bowl or large jar. Squeeze out as much liquid as possible from the vegetables and shells. Cover and set aside until ready to use. Can be refrigerated up to 5 days or frozen up to 6 months.
For the Cioppino:
6 Before cooking, scrub the mussels clean under cold water and remove any beards poking through the opening of the shells. Discard any mussels that are cracked or open. Add the clams to a bowl of cold water. Add 1 teaspoon salt and stir to agitate. Let the clams sit for at least 10 minutes so that they purge any sand inside the shells. Discard any clams that are cracked or open.
7 Preheat a large sauté pan or Dutch oven over medium heat. Add the olive oil and heat until shimmering. Add the fennel and onion and season with a pinch of salt. Cook, stirring, until the vegetables are soft and translucent, around 8 minutes. Add the garlic and cook, stirring, around 1 minute. Add the white wine, if using, and cook, stirring, until the liquid has reduced in volume by one half. Add the crushed tomatoes and cook, stirring until the liquid has reduced in volume by one quarter, around 6 minutes. Add the reserved shrimp stock and chile flakes and stir to combine. Taste for seasoning and adjust with salt and pepper as desired.
8 Bring the liquid to a simmer and layer in the grouper, shrimp, clams and mussels, in that order. Add the basil, cover with a lid, reduce the heat to medium-low and cook until the fish and shrimp are opaque and the clams and mussels have opened, around 8 minutes. Transfer the cioppino to individual serving bowls and garnish with reserved fennel fronds and a drizzle of olive oil. Discard any mussels and clams whose shells did not open. Serve on its own, with pasta, rice or crusty bread.
