Oven-Baked Haddock with Spinach and Tomatoes

Preheat your oven to 375°F (190°C). Lightly grease a 2-quart baking dish or casserole that is large enough to fit the haddock fillets in a single layer.

In a skillet, melt butter over medium heat. Add the onion and cook, stirring occasionally, until softened, about 5 minutes. Stir in the spinach and nutmeg, and cook for another 3 minutes.

Place the haddock fillets in the prepared dish. Spoon the spinach mixture evenly between the fillets. Scatter the drained tomatoes around the fillets and sprinkle with thyme, salt, and tarragon.

Bake, uncovered, for 20 to 25 minutes, or until the fish easily flakes when tested with a fork.

While the fish is baking, prepare the sauce: Add enough water to the reserved tomato juices to make 1 cup and set it aside. In the skillet, melt butter over medium heat. Stir in the onion and cook until softened, about 5 minutes. Pour 3/4 cup of tomato juice into the skillet and bring to a boil. In a separate bowl, whisk cornstarch into the remaining 1/4 cup of tomato juice, then add it to the skillet. Reduce the heat and simmer, stirring occasionally, until the sauce thickens slightly.

Pour the sauce over the baked fillets and serve.