Bring first 6 ingredients to a boil in a large saucepan over medium-high heat; reduce heat to medium-low, and cook, stirring often, 25 minutes or until thickened and bubbly. Remove from heat, and cool completely. Reserve 1 1/2 cups sauce; cover and chill. Set aside remaining sauce for basting.
Loosen skin from turkey without totally detaching skin; sprinkle salt evenly under skin, and carefully arrange 4 sage sprigs on each side of breast. Replace skin, and place turkey in a lightly greased 11- x 7-inch baking dish. Spread 3/4 cup maple-plum sauce evenly over turkey; cover loosely with aluminum foil.
Bake at 325° for 1 hour; uncover and bake 1 more hour or until a meat thermometer registers 170°, basting with remaining 3/4 cup maple-plum sauce every 15 minutes.
Remove turkey from baking dish; cool. Wrap in plastic wrap and then aluminum foil, and chill 8 hours. Serve turkey at room temperature. Cook reserved 1 1/2 cups maple-plum sauce until thoroughly heated; serve with turkey.
Maple-Plum Glazed Turkey Tenderloins: Substitute 2 (16-ounce) packages turkey tenderloins for breast. Place tenderloins on a rack in a broiler pan coated with cooking spray; sprinkle evenly with salt, omitting sage. Baste with 3/4 cup maple-plum sauce. Bake at 425° for 25 to 30 minutes or until done, basting often with remaining 3/4 cup maple-plum sauce.