How to Make It
Preheat oven to 425°F.
Heat oil in a large Dutch oven over medium-high. Add onions; sauté 6 minutes. Reduce heat to medium. Stir in 3 tablespoons thyme and 1/2 teaspoon salt; cook 10 minutes. Add wine to pan; cook 10 minutes or until onions are browned. Spread onion mixture in bottom of a roasting pan.
Combine remaining 1 tablespoon thyme, remaining 1 teaspoon salt, butter, and pepper in bowl. Loosen skin from breast by inserting fingers, gently pushing between skin and meat. Rub butter mixture under skin. Arrange breast, skin side up, over onion mixture. Bake at 425°F for 25 minutes. Pour 2/3 cup stock over turkey.
Reduce oven temperature to 350°F. Bake at 350°F for 1 1/2 hours or until a thermometer inserted into thickest portion registers 160°F, pouring about 2/3 cup stock over breast every 20 minutes (about 4 times, using all the stock before the end). Place turkey on a cutting board. Let stand, loosely covered with foil, 15 minutes (internal temperature will rise to 165°F).
Place roasting pan on burner over medium-high. Combine sherry and flour in a bowl. Stir sherry mixture into onion mixture; bring to a boil. Cook 10 minutes or until reduced to about 6 cups. Stir in parsley. Serve gravy with turkey. Remove skin before serving.