Black Cod Poached in Leeks and Crab Broth with Mashed Sweet Potatoes

Leeks in Crab Broth

Slowly softened leeks give the broth sweetness and body without cream. A restrained lemon finish brightens the shellfish flavor without overwhelming the cod.

Ingredients

• 3 large leeks, white and light green parts only
• 2 tablespoons unsalted butter
• 3 cups strained crab stock, gluten-free and preferably unsalted
• 1–2 teaspoons fresh lemon juice
• to taste fine sea salt and freshly ground black pepper

Instructions

1. Halve the leeks lengthwise and slice crosswise into 1/4-inch pieces. Wash thoroughly in several changes of water and drain.
2. Melt the butter in a wide, lidded sauté pan over medium-low heat. Add the leeks and a small pinch of salt. Cover and sweat for 10–12 minutes, stirring occasionally, until soft and glossy but not browned.
3. Add the crab stock and simmer gently, uncovered, for 5–8 minutes. The leeks should be very tender and the broth savory but still light enough to spoon around the fish.
4. Keep the broth in the pan for poaching the cod. After the fish is cooked and lifted out, taste the broth and add the lemon juice, salt, and pepper as needed.

Notes

• Use a mild crab stock rather than a heavily reduced or tomato-rich shellfish stock. If salty or overly concentrated, dilute with water before poaching.

Gently Poached Black Cod

Black cod's rich flesh stays succulent in a gentle poach. Cooking directly over the leeks flavors the fish while keeping its delicate surface intact.

Ingredients

• 4 portions black cod fillet, 6–7 ounces each, pin bones removed
• 1 batch leeks in crab broth, prepared above
• 1/4 teaspoon fine sea salt, or less if the broth is salty
• 1/4 cup flat-leaf parsley leaves, roughly chopped

Instructions

1. Pat the fish dry and season lightly with salt. Bring the leeks and broth to a bare simmer in the wide sauté pan.
2. Nestle the fillets over the leeks, skin-side down if skin-on. The broth should reach roughly halfway up the fish; add a little hot water if needed.
3. Cover and reduce the heat to low. Poach gently for 10–15 minutes, depending on thickness, without letting the broth boil vigorously.
4. Check the thickest part with an instant-read thermometer and cook to 145°F. The flesh should be opaque and separate into moist, broad flakes under gentle pressure.
5. Lift the fish carefully with a wide spatula. Finish seasoning the broth as directed in its recipe, then serve with the leeks, broth, and parsley.

Notes

• Keep the fish in a single layer for even cooking. If the skin is not appealing after poaching, gently slip it off before plating.

Smooth Mashed Sweet Potatoes

Orange-fleshed sweet potatoes provide a naturally sweet counterpoint to the shellfish broth. Steaming keeps their flavor concentrated and avoids a waterlogged mash.

Ingredients

• 2 pounds orange-fleshed sweet potatoes, peeled and cut into 1-inch chunks
• 3 tablespoons unsalted butter
• 2–4 tablespoons hot water, as needed
• 1/2 teaspoon fine sea salt, plus more to taste

Instructions

1. Set a steamer basket over simmering water. Add the sweet potatoes, cover, and steam for 20–25 minutes, until completely tender when pierced.
2. Transfer to a warm saucepan and let excess steam escape for 1–2 minutes.
3. Pass through a potato ricer or mash thoroughly. Fold in the butter and salt, then add hot water a tablespoon at a time until smooth and softly spoonable.
4. Taste and adjust the salt. Hold covered over very low heat, stirring occasionally, until the fish is ready.

Notes

• For an especially smooth finish like the pictured mash, briefly process the cooked sweet potatoes with the butter and just enough hot water to loosen them.

Overall Timing / Workflow

The mash can hold while the fish cooks, so the delicate cod is served immediately rather than reheated.

Instructions

1. 0:00 — Put the steaming water on, peel and cut the sweet potatoes, and wash and slice the leeks.
2. 0:10 — Start steaming the sweet potatoes and sweating the leeks in separate pans.
3. 0:22 — Add the crab stock to the leeks and bring to a gentle simmer. Portion and season the fish; chop the parsley.
4. 0:30 — Nestle the fish into the broth and cover. Mash the tender sweet potatoes and keep warm.
5. 0:40–0:45 — Check the fish for doneness, finish the broth with lemon, and plate immediately.

Plating

A shallow bowl holds the broth around the fish, while serving the mash separately preserves its texture and the broth's clarity.

Instructions

1. Divide the soft leeks among four warm shallow bowls.
2. Place a cod portion over each bed of leeks and ladle the crab broth around it, leaving the top of the fish exposed.
3. Scatter parsley over the fish and leeks.
4. Serve the mashed sweet potatoes in warm side bowls or in a shared serving dish, making broad swirls with the back of a spoon.

Leftover Path

Storing the mash separately keeps it from absorbing the broth. Gentle reheating protects the fish's tender flakes.

Instructions

1. Refrigerate the fish with its leeks and broth in a shallow airtight container within 2 hours. Store the mash separately and use both within 2 days.
2. Reheat the fish, leeks, and broth in a covered saucepan over low heat until the fish reaches 165°F, avoiding a rolling boil.
3. Warm the mash separately with a splash of water, stirring until smooth and hot.
4. Alternatively, flake the leftover fish into the hot leek-and-crab broth for a simple soup, adding fresh parsley and a little lemon just before serving.