Heat the olive oil in a very large pot over medium heat. Add in the fennel, onion, shallots, salt, and pepper, and cook until the onions are translucent. This should take about 10 minutes or so. Add the garlic and chili flakes and cook for another couple of minutes.

Stir in the tomato paste. Then add in the can of diced tomatoes, wine, stock, and the bay leaf. Cover the pot and bring the mixture to a simmer. Reduce the heat to medium-low and cook for 30 minutes.

Add the crabs, mussels, and clams to the pot. Simmer gently until the crabs are cooked, and the mussels and clams have opened. Discard any mussels and clams that failed to open. Season the cioppino with salt and pepper, to taste. When you are ready to serve your crab cioppino, remove the bay leaf from the pot. Ladle the stew into soup bowls and serve with large pieces of toasted sourdough or French bread on the side for dipping. The bread is the starch in this dish and really adds to the overall experience.