You can easily double this recipe (in two baking pans) to feed a larger crowd. The components can be assembled ahead of time, but bake the fish right before serving. It is good served individually or family style, and will keep well on a buffet.
- ½ cup extra-virgin olive oil
- 2 medium onions, cut into thin rings
- 1½ teaspoons kosher salt
- 3 medium tomatoes, sliced ½ inch thick
- Four 6-ounce skinless halibut fillets, about 1½ inches thick
- 6 leafy sprigs fresh thyme
Preheat oven to 425 degrees. In a large skillet, heat ¼ cup of the olive oil over medium heat. When the oil is hot, add the onions, and season with 1 teaspoon of the salt. Cover, and cook, stirring occasionally, until onions are wilted, about 8 minutes.
In a 9-by-13-inch glass or ceramic baking dish, lay the onion slices in an even layer. Drizzle with 2 tablespoons olive oil, and season with ¼ teaspoon of the salt. Layer the tomatoes over the onions. Place the halibut fillets on top. Drizzle with the remaining 2 tablespoons oil, and season with the remaining ¼ teaspoon salt. Stick a thyme sprig on each piece of fish.
Cover tightly with foil, and bake until the tomatoes release their juices, about 10 to 15 minutes. Remove foil, and bake until the onions are caramelized in places and the fish is cooked through, about 10 minutes more. Serve hot.