Monkfish and Clam Bourride - Mediterranean fish soup

6 small (1 1/2- to 2-inch) red potatoes (3/4 pound)
2 large leeks (white parts only), cut crosswise into 1/4-inch-thick slices
1 (1-pound) piece monkfish fillet, cut into 2-inch chunks
3 tablespoons extra-virgin olive oil
1 large fennel bulb (sometimes called anise), stalks discarded and bulb halved lengthwise, cored, and thinly sliced lengthwise
1 cup thinly sliced shallots (4 medium)
4 garlic cloves, 3 thinly sliced and 1 halved crosswise
24 small hard-shelled clams (2 pounds) such as littlenecks (less than 2 inches wide), scrubbed well (Trader Joe's has these ready to go in their frozen food section)
1/2 cup dry white wine
1/2 cup water
1 teaspoon dried hot red pepper flakes
1 teaspoon finely grated fresh lemon zest
8 fresh basil leaves, chopped
2 tablespoons chopped fresh parsley
4 (3/4-inch-thick) slices crusty bread (about 4 inches wide), toasted


Accompaniments: aïoli and green olive tapenade (Trader Joe's)
Garnish: 8 whole fresh basil leaves

Quarter potatoes, then cover by 1 inch with salted cold water in a 3-quart saucepan and simmer, covered, until just tender, 7 to 10 minutes. Drain in a colander, then cool.

Wash leeks in a bowl of cold water, agitating water to loosen any sand, and lift leeks from water to a sieve to drain. Pat dry.

Pat monkfish dry and season with salt and pepper. Heat oil in a deep 12-inch heavy skillet over moderately high heat until hot but not smoking, then sear monkfish lightly on all sides until golden, about 2 minutes total (fish will not be cooked through). Transfer fish to a plate using tongs.

Heat 2 tablespoons oil from slow-braised tomatoes in skillet over moderately high heat until hot but not smoking, then sauté leeks, fennel, and shallots, stirring, until softened and edges begin to brown, 4 to 6 minutes. Add sliced garlic and sauté, stirring, until fragrant, about 2 minutes.

Add clams, wine, water, red pepper flakes, zest, and tomato halves and cook, covered, until clams are fully open, 6 to 10 minutes, checking every minute after 6 minutes and removing clams as they fully open. (Discard any clams that have not opened after 10 minutes.) Using tongs, transfer clams to a large bowl or soup tureen.

Add monkfish and potatoes to skillet and simmer, covered, until fish is just cooked through, 4 to 6 minutes. Remove from heat and stir in basil and parsley. Season with salt and pour over clams.

While monkfish is cooking, rub one side of each toast with a cut side of halved garlic clove. Divide bourride among 4 shallow bowls. Add a garlic toast and top with a spoonful each of aïoli and tapenade.