How to Make It
To prepare brine, bring 3 cups water and next 4 ingredients (through 1/3 cup salt) to a boil in a large saucepan; cook 2 minutes or until salt dissolves. Remove from heat; let stand 10 minutes. Place brine and remaining 13 cups water in a brining bag.
To prepare turkey, remove giblets and neck from turkey; reserve. Trim excess fat; add turkey to brine. Refrigerate 18 to 24 hours, turning occasionally.
Preheat oven to 425°F.
Remove turkey from brine; discard brine. Pat turkey dry. Combine butter, chopped thyme, rind, 1 1/2 teaspoons salt, and pepper in a bowl. Starting at neck cavity, loosen skin from breast and drumsticks by inserting fingers, gently pushing between skin and meat. Rub butter mixture under loosened skin. Lift wing tips up and over back; tuck under turkey. Place 5 thyme sprigs, lemons, and onion in body cavity. Secure legs with kitchen twine.
Place turkey on the rack of a roasting pan coated with cooking spray. Place neck in bottom of pan; place rack with turkey in pan. Add 1/2 cup water to pan. Bake at 425°F for 45 minutes. Baste with half of oil.
Reduce oven temperature to 350°F (do not remove turkey from oven). Bake at 350°F for 1 hour and 15 minutes. Rotate turkey from front to back; baste with remaining half of oil. Bake at 350°F for 10 to 20 minutes or until a thermometer inserted into thickest part of thigh registers 160°F. Remove from oven; place turkey on a cutting board. Let stand, loosely covered with foil, 20 minutes (internal temperature will rise to 165°F). Remove skin before carving. Reserve pan drippings and neck for gravy, if using.