Step 1

Heat 2 tablespoons olive oil in a large high-sided skillet (at least 10 inches) or Dutch oven over medium heat until shimmering. Add 1 diced small fennel bulb, 1 coarsely chopped medium leek, 1 diced medium plum tomato, 1 diced large shallot, 2 thinly sliced garlic cloves, and 1/2 teaspoon of the kosher salt. Cook, stirring occasionally, until the vegetables are tender and translucent, about 7 minutes.

Step 2

Stir in 1 tablespoon tomato paste, 2 large pinches saffron threads, 1/2 teaspoon fennel seeds, 1/4 teaspoon black pepper, 1 wide strip fresh orange peel, and 1 dried bay leaf. Cook, stirring often, until fragrant and the tomato paste darkens in color, about 2 minutes.

Step 3

Stir in 1/2 cup dry white wine and simmer until the wine is almost completely evaporated, about 2 minutes. Stir in 1 quart fish stock, 4 fresh parsley sprigs, and the remaining 1 teaspoon kosher salt. Increase the heat to high and bring to a boil. Reduce the heat to maintain a lively simmer and cook for 30 minutes to reduce slightly and let the flavors meld.

Step 4

Turn off the heat. Remove and discard the bay leaf and parsley stems. Working in batches if needed, transfer the mixture to a blender and blend until smooth. Pour the blended mixture through a fine-mesh strainer back into the skillet. Press on the solids to extract as much of the liquid as possible until only a paste is left in the strainer. Scrape the underside of the strainer into the skillet. Discard the contents of the strainer.

Step 5

Taste the broth and season with more kosher salt as needed; it should be very well-seasoned. Return to a boil over medium-high heat. Add 2 1/2 pounds cut white fish fillets, starting with the thickest pieces and ending with the thinnest. Make sure the fish is mostly submerged in liquid and return to a lively simmer.

Step 6

Gently stir again to move the fish at the top closer to the bottom. Turn off the heat. Cover and let sit for 3 to 5 minutes to let the residual heat gently finish cooking the fish (the fish should be opaque).

Step 7

Serve in bowls garnished with chopped fresh parsley leaves, with toasted bread and garlic aioli on the side. Alternatively, gently transfer the fish to a serving platter with a slotted spoon and garnish with chopped parsley. Place toasted bread in shallow serving bowls (the bread can be smeared with aioli, or the aioli can be served on the side). Ladle broth over the bread, then top with fish.