Preparing the Fillets

1. Prepare a brine for your fish. You can vary the mixture to suit your own taste, but for every gallon of water you'll need roughly 1 to 1 1/4 pounds of coarse salt and at least 1/4 pound of sugar to mellow the salt's harshness. Simmer the ingredients in a large pot until the salt and sugar are dissolved, then pour your brine into a food-safe container and refrigerate it.

2. Feel the haddock fillets with your fingertips, to ensure all the bones have been removed. If your fillets are skin-on, wipe them with a clean paper towel to remove any loose scales. Immerse the fillets in your brine, covering them with a plate to keep them underwater. Soak them in the brine for 8 to 10 hours.

3. Drain the fillets and rinse them, then let them sit in cold, fresh water for 10 minutes. This leaches a small amount of salt from the outer surface of the fillets, where it's strongest. Drain the fillets again, and carefully pat them dry with clean paper towels.

4. Place a wire rack over a baking sheet, and arrange the fillets on the rack. Leave room between them for air to circulate. Clear a shelf in your refrigerator, and slide the pan of fish onto it. Refrigerate them, uncovered, overnight. The dry air of the refrigerator will form a thin skin, or pellicle, that helps the fillets retain flavor from the smoke.

Smoking the Fillets

1. Prepare your smoker according to the manufacturer's instructions, using light-tasting alder or fruit woods, and set it for 185 to 200 degrees Fahrenheit. If you're using a charcoal smoker, adjust the vent and damper to the lowest temperature you can maintain. Usually, that's between 200 and 225 F.

2. Arrange the haddock fillets on the smoker's racks, leaving room between them for the smoke to circulate. Close the smoker.

3. Hot-smoke the haddock fillets until they reach an internal temperature of 150 F, which takes approximately 2 hours, depending on their thickness.

4. Cool the fillets completely, then wrap them in airtight packaging and freeze them for later use.