Make the rouille: Puree the mayonnaise, roasted red peppers, olive oil, lemon juice, garlic and a pinch of salt in a blender until smooth. Transfer to a small bowl; refrigerate until ready to serve.
Prepare the bouillabaisse: Grate the tomato flesh on the large holes of a box grater down to the skins; reserve the skins separately. Peel and devein the shrimp, reserving the shells and tails for the broth; clean and debeard the mussels. Refrigerate the seafood until ready to use.
Make the broth: Heat 3 tablespoons olive oil in a large pot over medium-high heat. Add the shrimp shells and tails and cook, stirring, until bright red, about 3 minutes. Stir in the tomato paste until incorporated, about 30 seconds. Add the clam juice, 4 cups water, the reserved tomato skins, the orange zest and 1/4 cup of the sliced fennel. Bring to a boil, then reduce the heat to medium; simmer until the liquid is reduced to about 4 cups, 12 to 15 minutes. Strain the broth through a fine-mesh sieve set over a bowl, pressing on the solids to extract the liquid; reserve the broth.
Wipe out the pot and heat the remaining 3 tablespoons olive oil over medium heat. Add the remaining fennel, the shallot, garlic and a pinch of salt; partially cover and cook, stirring occasionally, until the fennel begins to soften, about 5 minutes. Add the reserved grated tomato flesh and cook, stirring, until slightly thickened, about 2 minutes. Stir in the saffron, then add the wine and simmer until the liquid is reduced by about two-thirds, about 4 minutes. Add the reserved broth and return to a simmer.
Add the mussels to the pot; cover and cook 4 minutes. Add any thick pieces of fish and cook, covered, 2 minutes. Add the remaining fish and the shrimp and cook, covered, until the mussels open and the fish and shrimp are just cooked through, 3 to 4 more minutes. (Discard any mussels that do not open.) Season with salt and pepper.
Spread the baguette with the rouille and serve with the bouillabaisse. Sprinkle with parsley.
Photograph by Con Poulos
Recipe courtesy of Food Network Magazine