Mackerel with Puttanesca and Potatoes

From Fish Without a Doubt: The Cook's Essential Companion by Rick Moonen and Roy Finamore.

I like making this satisfying, warming casserole in individual gratin dishes, but you can just as easily make it in one larger dish — just increase the cooking time by 5 minutes.
Make the puttanesca and boil the potatoes a day ahead, and the dish will be a snap to put together.
Serves 4

Accept Substitutes

Try this with filleted fresh sardines.
Olive oil
1 pound white or red-skinned
potatoes, boiled until just tender, peeled, and sliced
Coarse salt
4 tablespoons dry vermouth
4 (6- to 7-ounce) pieces mackerel fillet
Freshly ground white pepper
2 cups Puttanesca Sauce (see below)
1 cup dry bread crumbs
2 tablespoons chopped fresh parsley
2 garlic cloves, minced or put through a press
1. Heat the oven to 450 degrees.
2. Oil four individual gratin dishes (2-cup capacity) generously with olive oil. Divide the potatoes among the dishes and season with salt. Sprinkle 1 tablespoon vermouth into each dish.
3. Season the fish with salt and white pepper. Lay the fillets on top of the potatoes and spread 1/2cup of the puttanesca sauce over each, covering it completely.
4. Mix the bread crumbs, parsley, garlic, and 2 teaspoons olive oil together in a small bowl. Sprinkle the crumbs over the casseroles, dividing them as evenly as you can.
5. Slip the casseroles into the oven and bake until the potatoes are piping hot and the fish is cooked through, about 12 minutes.

Puttanesca Sauce

This pasta sauce is actually a great accompaniment to fish. It’s the start of a fine fish casserole too.
Makes about 3 cups
1/4 cup olive oil
1 cup chopped onion
1/4 cup chopped garlic
8–10 anchovy fillets, chopped
Crushed red pepper
3 cups chopped tomatoes (Pomì preferred)
1/2 cup sliced kalamata or other black olives
1/4 cup drained capers
1. Heat a medium saucepan over medium-high heat. When the pan’s hot, add the oil and the onion and cook, stirring often, until the onion is translucent, about 7 minutes. Add the garlic and continue cooking until the onion is turning gold at the edges, another 3 to 4 minutes. Add the anchovies and a good pinch of crushed red pepper and cook, stirring, until the anchovies start to melt, about 1 minute. Add the tomatoes, olives, and capers and bring to a simmer. Reduce the heat and simmer the sauce for 15 minutes, or until thick and fragrant.
2. You can use the sauce now or refrigerate it, covered, for up to 1 week.
From FISH WITHOUT A DOUBT: The Cook's Essential Companion by Rick Moonen and Roy Finamore.