Pat turkey dry using paper towels; place turkey, breast side down, on a cutting board. Using kitchen shears, cut along either side of backbone to separate backbone from turkey. Discard backbone, or reserve for making stock. Flip turkey breast side up. Using the heels of your hands, firmly press down against breastbone until it cracks and turkey flattens. Arrange turkey breast side up on a wire rack, and place rack inside an 18- x 13-inch rimmed baking sheet; tuck wing tips underneath turkey. Loosen turkey skin from breast, thighs, and drumsticks by sliding your fingers underneath the skin. Stir together salt, ginger, and white pepper in a small bowl. Rub two-thirds of the salt mixture (about 2 ½ tablespoons) evenly beneath skin of breast, thighs, and drumsticks; rub remaining salt mixture (about 1 tablespoon) over wings and skin of breast, thighs, and drumsticks. Refrigerate, uncovered, for 24 hours.

Remove turkey from refrigerator; let stand at room temperature for 1 hour. Arrange onions, carrots, and celery in bottom of a second rimmed baking sheet. Place turkey on an oven-safe wire rack, and set over vegetables on baking sheet.

Preheat oven to 450°F with oven rack in middle position. Stir together butter and sesame oil in a small bowl until thoroughly combined. Rub 2 to 3 teaspoons butter mixture over wings, and rub remaining butter mixture underneath turkey skin and over breast, thighs, and drumsticks.

Roast turkey in preheated oven until an instant-read thermometer inserted into center of thigh registers 185°F, breast registers 155°F, and skin is crispy and golden brown, 1 hour to 1 hour and 10 minutes. Tent turkey using aluminum foil during last 15 minutes of roasting if skin begins to get too dark. Remove turkey; let stand 30 minutes before carving.