Cooking fish at a low temperature in a covered pot is a nearly foolproof way to achieve perfectly cooked fish, since the heavy Dutch oven holds in moisture and allows the fish to cook through gently and evenly.
This method is also a wonderful way to concentrate flavor, meaning that a minimum of ingredients can make a big impact. We started by browning sliced garlic in oil, which mellowed its flavor and infused the dish with warm aromatic notes.
Cherry tomatoes became soft and sweet with the gentle cooking. Capers provided briny bites, and thyme gave the dish an herbal base note.
While the halibut rested, we finished the sauce by cooking off some of the excess liquid on the stovetop. Sea bass and swordfish steaks are good substitutes for the halibut.