In a small saucepan, simmer maple syrup, duck fat or oil, rosemary and salt until the fat melts and the maple syrup thickens slightly, about 5 minutes. Let cool.

Remove the skin from the turkey (keeping it intact, if you’d like to roast it separately). Refrigerate until you are ready to roast it. Place the turkey in a large bowl and pour the cooled maple mixture over it, turning to coat pieces with syrup. Cover and refrigerate overnight.

Cook using an immersion circulator (“sous-vide machine”)

Using a sous-vide machine, heat a large pot or heatproof container of water to 145 degrees. Transfer turkey to a reusable silicone sous-vide bag or resealable plastic bag, laying breasts end-to-end so the thin side of one is against the thick side of the other. Discard marinade. Slowly lower the bag into the water, allowing any air to escape. Weigh down the bags; an upside-down metal steamer basket or a metal bowl work well for this, topped with a metal spoon or tongs for extra weight, if needed.

Cook until the turkey reaches 145 degrees when checked in the center with a meat thermometer, 2 1/2 to 3 hours. Once the turkey is at 145 degrees, leave it in the bag in the water for an additional 15 minutes to pasteurize it. Serve immediately with crisp turkey skin, if you like, or leave turkey breast in the water at 145 degrees for up to 12 hours total.