Rinse the fish under cold running water and pat dry with paper towels. Rub the halibut steaks on both sides with 2 teaspoons sea salt. Combine the 1 cup parsley, the chopped mixed herbs, four-fifths of the bay leaves, the marigolds, if using, and the garlic and rub onto both sides of the fish. Place the fish in a deep baking dish, cover, and refrigerate for at least 30 minutes, or up to 24 hours.
Preheat the oven to 400°F. Pour the wine over the fish and cover the baking dish with foil. Bake for 15 to 20 minutes, until the fish is opaque throughout and comes away from the bone when tested with a knife. Transfer the halibut to a platter and cover to keep warm. Pour the pan juices into a small saucepan and reduce over medium heat to about 1/4 cup.
Meanwhile, in another small saucepan, heat 1 tablespoon of the butter until it bubbles enthusiastically. Add the finely chopped rosemary, thyme, and the remaining bay leaves. Cook for 2 minutes. Add the rest of the butter and let it melt, then add the tarragon, the remaining 2 teaspoons parsley, and the lemon zest. Simmer for 3 to 4 minutes; do not boil. Add the lemon juice, the reduced marinade, and salt and pepper to taste. Strain the sauce and discard the herbs.
Brush off the herbs from the fish. Place a halibut steak on each plate, and place a marigold, if using, on the side. Pour a little rosemary-lemon butter over each halibut steak and serve.
Variation: When increasing the quantity of fish, you do not need to increase the amount of wine and herbs accordingly. Use enough herbs to cover the fish and enough wine to cover the bottom of the pan.
Bake until the fish is opaque throughout and comes away from the bone when tested with a knife. If you are cooking a large halibut, you should use an instant-read thermometer; the fish is done when the interior temperature has reached 125°F.