Chef John's Fisherman's Pie

Recipe View Preheat the oven to 375 degrees F (190 degrees C).

Recipe View In a large saucepan, cover the potatoes with salted water and bring to a boil. Cook until very tender, about 20 minutes. Drain well and return to the saucepan.

Recipe View Add 3 tablespoons of butter to the potatoes and mash until smooth. Season generously with nutmeg, salt, black pepper, and cayenne pepper. Gradually mash in 1/2 cup of milk until light and fluffy. Set aside. (Total time: 25 minutes)

Recipe View Heat olive oil in a large Dutch oven or skillet over medium-high heat. Add spinach and a pinch of salt. Cook, stirring occasionally, until just wilted, about 1 minute. Transfer to a bowl lined with paper towels to remove excess moisture.

Recipe View In a saucepan, melt 3 tablespoons butter over medium heat. Whisk in flour and cook, stirring constantly, until a smooth, light golden paste forms, about 2 minutes. Add minced garlic and cook until fragrant, about 30 seconds. (Total time: 3 minutes)

Recipe View Gradually whisk in 1 cup of cold milk into the flour mixture until smooth. Cook, stirring constantly, until thickened, about 3 minutes. Whisk in the remaining 1 cup of milk and lemon zest. Bring to a gentle simmer, whisking constantly, and season with salt to taste. Reduce heat to low and keep warm.

Recipe View Grease an 8x12-inch casserole dish with 1 tablespoon of butter. Season the buttered pan with salt, black pepper, and cayenne pepper.

Recipe View Arrange the cod fillets in a single layer in the prepared dish. Season the tops of the fillets with salt, black pepper, and cayenne pepper. Spread the wilted spinach evenly over the fish and drizzle with lemon juice. (Total time: 5 minutes)

Recipe View Pour the white sauce evenly over the spinach. Gently tap and shake the dish to release any trapped air bubbles.

Recipe View Spoon the mashed potatoes evenly over the white sauce, creating a smooth, complete covering. (Total time: 3 minutes)

Recipe View Place the dish on a rimmed baking sheet to catch any spills.

Recipe View Bake in the preheated oven until bubbling and heated through, about 40 minutes. Turn on the oven's broiler and broil until the potato crust is golden brown, about 2-3 minutes. The fish should flake easily with a fork. (Total time: 43 minutes)

Recipe View Let stand for 10 minutes before serving. Garnish with fresh chives.