On a work surface, place turkey, breast side up. With your fingertips, separate skin from breast and thigh meat, being careful not to tear skin.
Place turkey, breast side up, in a roasting pan. Season the inside of the turkey with 15 ml (1 tablespoon) of seasoning salt. Rub remaining salt under skin, with an emphasis on breast and thighs. Cover with plastic wrap and refrigerate for three days.
With the rack in the lowest position, preheat the oven to 220 °C (425 °F).
In a large roasting pan with a wire rack, place turkey, breast side up. Blot turkey skin with paper towels and brush with 60 ml (¼ cup) of butter.
Pour half of the apple juice, broth and Marsala at the bottom of the pan. Roast for 30 minutes. Reduce oven temperature to 170 °C (325 °F) and continue cooking for about 1 hour and 30 minutes or until a meat thermometer inserted into the thigh without touching bone reads 82 °C (180 °F). Add broth, if needed. Place turkey on a serving dish and let rest for about 30 minutes, without covering with foil.
Deglaze pan with remaining apple juice (375 ml/1 ½ cups) and skim most fat with a large spoon. Set aside in a bowl.
In a saucepan, melt remaining butter (15 ml/1 tablespoon). Add flour and cook while stirring until mixture begins to brown, about 2 minutes. Add cooking juices and honey and bring to a boil, stirring with a whisk. Simmer for about 5 minutes, until sauce thickens. Adjust seasoning.
Slice turkey and serve with sauce and Old-fashioned Apple and Sausage Stuffing (see recipe).