Creamy Cod and Potato Gratin

1. Stage

Place potatoes in a large pot of well-salted water and bring to a boil over high heat. Reduce heat and simmer gently until tender, about 20 minutes.

2. Stage

While potatoes simmer, trim, bone, and cut the cod fillets across into 2-inch pieces.

3. Stage

Drain potatoes well and return to the pot. Add a pinch of cayenne, salt, and 4 tablespoons butter. Mash until smooth.

4. Stage

Preheat the oven to 450 degrees F (230 degrees C). Grease 2 individual-sized casserole or baking dishes with 1 tablespoon butter. Place both dishes on a baking sheet.

5. Stage

Transfer about 2/3 cup of the mashed potatoes into each of the prepared dishes. Smooth out evenly and make a shallow depression with a spoon down the middle. Set aside.

6. Stage

Heat remaining 2 tablespoons butter in a deep 10-inch skillet over medium-high heat. Cook the shallots in the hot butter with a pinch of salt until they just start to turn golden, 3 to 4 minutes. Add cream, lemon zest, and a pinch of cayenne, and bring to a simmer. Add cod and wait for the sauce to come back to a simmer. Cook for 1 minute, while basting with the sauce; turn and cook for 1 minute more.

7. Stage

Pour in lemon juice and turn off the heat; stir for about 30 seconds.

8. Stage

Divide the pieces of cod over the potato. Add enough sauce to just cover the fish and return the pan to the stove.

9. Stage

Bring sauce to a boil over medium-high heat and cook until the sauce reduces and thickens, 1 to 2 minutes. Turn off the heat and stir in tarragon.

10. Stage

Spoon the thickened sauce over the cod. Add a light dusting of Parmigiano-Reggiano cheese.

11. Stage

Bake in the center of the preheated oven until cod is cooked through and the sauce is browned and bubbling, 10 to 15 minutes. Let rest for 5 minutes before serving. Unknown