How to Make It
In a large enameled cast-iron casserole, heat 2 tablespoons of the olive oil. Add the fennel, leek, onion and celery and cook over moderate heat, stirring occasionally, until the vegetables are softened, about 8 minutes. Stir in the garlic and saffron and cook until fragrant, about 2 minutes. Add the Pernod and cook over moderately high heat until the liquid is evaporated, about 2 minutes. Add the wine and vermouth and cook until the liquid is reduced by about half, about 8 minutes. Add the tomatoes and cayenne and simmer over moderate heat until the liquid is reduced by half, about 5 minutes.
Meanwhile, in a large skillet, heat 2 tablespoons of the olive oil. Add the fish bones to the skillet and cook over moderately high heat, turning once, until browned, about 5 minutes. Transfer the bones to the casserole along with 2 cups of water. Cover partially and simmer over moderately low heat for 30 minutes. Let the sauce cool slightly, then discard the fish bones. Using an immersion blender, puree the sauce, then strain through a fine-mesh sieve into a medium saucepan. Add the 2 teaspoons of lemon juice, season with salt and keep warm.
Meanwhile, preheat the oven to 375°. Season the fish with salt and refrigerate, uncovered, for 30 minutes. In a large ovenproof nonstick skillet, heat the remaining 2 tablespoons of olive oil until shimmering. Add the fish and cook until browned on the bottom, about 3 minutes. Flip the fillets and transfer the skillet to the oven. Bake for 6 to 8 minutes, until the fish is opaque and just cooked through.
Ladle the sauce into 4 shallow bowls and top each with a cod fillet. Spoon the tapenade over the fish and drizzle with lemon juice and olive oil. Serve immediately.