I love raisins with fish—they have the perfect balance of sweet and acid, which really accentuates the flavors of not-so-strong-flavored fish, a.k.a. slightly bland-tasting halibut. I like to use larger pieces of halibut here as they are easier to deal with than smaller fillets. These larger pieces can be divided at the table.
Preheat the oven to 300 degrees.
For the coating, melt 2 tablespoons of the butter and combine it with the raisin paste in a small bowl. Add the panko, ginger, mace, and orange zest and mix well. You should have a thick, slightly sticky paste.
Pat the halibut as dry as possible, then press the breading paste into the top of the fish and gently massage it so that it sticks.Heat a large, ovenproof sauté pan over medium-high heat. Melt the remaining 1/2 tablespoon butter in the pan, then place the halibut, breading side down, in the butter. Cook, without moving the fish, until the coating begins to brown around the edges, about 4 minutes. Transfer the whole pan into the oven and cook for 20 minutes for a piece of halibut that is 1 1/2 inches thick. This will ensure that the breading continues to cook evenly and becomes very crispy while protecting the fish and keeping it moist.
Once the halibut is done, it will begin to flake apart if slight pressure is applied to the side. Using a spatula, gently turn the fish out of the pan and onto the serving plates with the breaded side facing up.