Start with a mild, flaky white fish—we went with Atlantic cod, but halibut, black cod, or even skate wing can also be substituted here. Just be sure to reduce the cooking time accordingly for thinner fillets. To prevent sticking, use a large, heavy-duty skillet and a mixture of olive oil and butter to sear the cod. I like this textured stainless-steel pan: the light color makes it easy to see when the butter has fully browned, and the textured interior keeps the delicate fillets from adhering and tearing. A good-quality, unscratched nonstick skillet or even a lighter-weight cast-iron one will also get the job done, but be prepared to rely on your nose when toasting butter in a dark-colored pan.
Let the Fillets Steam
Sear the fillets until the exterior is just set and lightly browned, then transfer them to a warm plate and cover. The residual heat will finish cooking the fish without drying it out or causing it to flake apart. The brown-butter tomato sauce comes together quickly, so place the fillets by the stove to keep them warm and at the ready for finishing the dish.
Brown the Butter
Since butter is one of the main flavoring agents in this sauce, use it as an opportunity to break out the good stuff. Look for an unsalted European-style cultured butter—I like the ones by Vermont Creamery, D’Isigny, Kerrygold, Échiré, and Plugra. Once the butter has melted, be sure not to turn away from the stove—much like caramel, butter can go from perfectly browned to burned to the point of no return in a flash. Wait patiently until you see the milk solids sink to the bottom of the skillet and turn pale golden. As the particles brown, use a wooden spoon or spatula to scrape the bottom of the pot, stirring frequently so that they toast evenly.
Sauté the Aromatics
Once the butter takes on that telltale golden hue, add the shallots. The cool, wet vegetable will drop the temperature of the oil and prevent the solids from browning further. Cook until the shallots just begin to soften and lose their raw flavor without allowing them to color. Add the garlic and cook for a few more seconds, once again just to soften and infuse the butter with their fragrance and flavor.
Barely Cook the Tomatoes
Cut each of the cherry and grape tomatoes in half, both to make them easier to eat and also to encourage them to release their sweet-tart juices into the sauce. Add them to the hot butter mixture and give the skillet a good shake to combine. Cook, shaking occasionally, until the tomatoes soften and just begin to turn jammy.
Finish with Vermouth
A final splash of vermouth brings the juices together and adds another layer of flavor to the sauce. The fortified wine’s acidity offsets the richness of the brown butter, and its faintly bitter, botanical notes contrast nicely against the sweet tomatoes. Cook just long enough to boil off the alcohol (use your nose again), then quickly remove from the heat. You don’t want to over-reduce and cause your silky, emulsified sauce to separate (although if it does break, don’t fret; it will still be delicious). Once the sauce is finished, spoon it over the fish on a large rimmed platter or a shallow bowl, then add a few parsley leaves for color and freshness. Serve with plenty of crusty bread for sopping up all the juices and a medium-bodied white wine to wash everything down. See the full recipe for Skillet Cod with Brown-Butter Tomato Sauce
