Here in the Pacific Northwest Halibut is serious business, and it's no wonder either. It's flesh is very firm but somehow equally flaky and has a mild, succulent flavor.
Preheat oven to 450°. While waiting, mix dijon and garlic in a small bowl and coat the halibut filets with the mustard mixture. Sprinkle a generous pinch of salt and cracked pepper onto the filets and place a tablespoon of butter on top. Let rest while the oven heats up.
When the oven is hot, position a rack near the top of the oven, and roast the fish skin side down in a cast-iron skillet or sheet pan for 10-12 minutes.
After that, switch the oven to broil and continue to cook the fish until the top is lightly browned, about 2-3 minutes. Watch carefully to prevent burning.
Serve with some chopped dill or tarragon and lemon wedges.
Notes
Let the Halibut sit out at room temperature for 30-45 minutes before cooking. The filets can be very thick so it will cook more evenly this way.