Fisherman's Pie

For the potatoes:

3 russet potatoes, peeled and cut into chunks

3 tablespoons butter

1 pinch grated nutmeg

salt and ground black pepper to taste

1 pinch cayenne pepper, or to taste

1/2 cup milk

For the spinach:

2 teaspoons olive oil

12 ounces baby spinach leaves

For the sauce:

3 tablespoons butter

3 tablespoons all-purpose flour

2 cloves garlic, minced

2 cups cold milk, divided

For the rest:

1 tablespoon butter

salt and ground black pepper to taste

1 pinch cayenne pepper, or to taste

2 pounds boneless cod fillets

1/2 lemon, juiced

1 tablespoon chopped fresh chives for garnish (I don't bother)

Optional: other vegetables you might want in a Shepard's pie style dish (I like mushrooms, but peas, carrots, or green beans might work too).

1. Bring a large saucepan of salted water and to a boil; add russet potatoes to boiling water and cook until very tender, about 20 minutes. Drain well. (You can also do this in the microwave if that is how you prefer to cook mashed potatoes). Mash in 3 tablespoons butter until thoroughly combined. Season with nutmeg, salt, black pepper, and cayenne pepper to taste. Mash 1/2 cup milk into potato mixture until smooth.
2. Drizzle olive oil in a large Dutch oven or wok or whatever you use, over medium-high heat, add spinach, and season with a big pinch of salt. Cook, stirring occasionally, until spinach has wilted, about 1 minute. Transfer to a bowl lined with paper towels to wick away excess moisture. Alternatively (as I do) just use frozen spinach, thawed and drained and then cooked with some olive oil.
3. Heat 3 tablespoons butter and flour in a saucepan over medium heat; whisk mixture to a smooth paste. Cook, stirring constantly, until mixture has a nutty smell and is slightly browned, about 2 minutes. Add chopped garlic; whisk until fragrant, 10 to 20 seconds.
4. Whisk 1 cup cold milk into flour mixture; cook until thickened. Whisk in remaining 1 cup milk (and if you want it, some lemon zest, but I find this makes the recipe too lemony). Bring white sauce to a gentle simmer, whisking constantly; season with salt. Turn heat to very low and keep sauce warm.
5. Preheat oven to 375 degrees F. Grease an 8x12-inch casserole dish with 1 tablespoon butter.
6. Season buttered pan with salt, black pepper, and cayenne pepper. Lay boneless cod fillets into the pan in a single layer. Season tops of fillets with more salt, black pepper, and cayenne pepper. Spread spinach evenly over fish and drizzle with lemon juice. If you're adding extra vegetables, mix them with the spinach or place them above or below it in a thin layer. Spoon white sauce over spinach; give casserole dish several taps and shakes to eliminate bubbles.
7. Drop mashed potatoes by heaping spoonfuls over the casserole and spread smoothly to cover. If you brush some melted butter or olive oil on top of them you'll get a delicious crust too. Place dish onto a rimmed baking sheet to catch spills.
8. Bake in the preheated oven until bubbling, about 40 minutes. Turn on oven's broiler and broil until potato crust has a golden brown top, about 2 minutes. Fish should flake easily. Let stand 10 minutes before serving. Garnish with a sprinkle of chives if you'd like.

(Adapted from Chef John's Fisherman's Pie, which I found on Allrecipes.com)