Detach the crab legs from the body by hand. With a mallet, crack the legs and claws. Holding each crab from underneath, lift off and discard the hard top shell. Turn the crab over; lift off and discard the triangular tail flap and the feathery gills along both sides. Quarter the body and pick out the meat. Reserve the body shells for the fish stock if desired.
Heat a large, wide 8-quart pot over moderately low heat. Add the olive oil. When the oil is hot, add the onion, celery, fennel, garlic, and chile flakes. Sauté until the vegetables are soft and sweet, 10 to 15 minutes. Add the tomato and wine, raise the heat to high, and bring to a boil. Add the fish stock, bay leaves, basil, and salt to taste. Simmer gently until reduced to the texture of a thin tomato sauce, 15 to 20 minutes.
Add the clams and mussels. Cover and cook over high heat until the shellfish begin to open. Add the crab legs and the shrimp. Cover and simmer for about 2 minutes, then add the halibut and the shelled crab meat. To keep the halibut in large chunks, don’t stir it into the cioppino; cover the pot and let the fish steam on the surface until white throughout, about 7 minutes. Serve immediately in large bowls, dividing the fish and shellfish evenly and ladling the broth around.
Enjoy with Cakebread Cellars Chardonnay Reserve.