How to Make It
Remove the giblets, then rinse the turkey. Dry with paper towels. Rub the cavity with the salt. Cut 2 of the oranges into 2-inch chunks. Set aside a few sage sprigs for garnish later. Place the remaining sage, cut-up oranges, and garlic in the cavity. Loosen the skin from the breast and spread the cheese under the skin. Tuck the wings under the back; tie the legs together. Arrange the carrots and leeks in the roasting pan to create a "rack" and place the turkey on it; rub with oil. (The turkey can be prepared to this point up to 1 day ahead. Cover the pan with plastic wrap and refrigerate.)
Heat oven to 350º F. Roast for 1 hour. Place a foil tent over the turkey and continue roasting for 2 1/2 to 3 hours more or until an instant-read thermometer registers 180º F when inserted in the breast.
Remove the roasting pan from the oven. Carefully move the turkey to a platter, pouring any cavity juice back into the pan. Cover with foil to keep warm. Set oven to 500º F. Cut the remaining 6 oranges into quarters and arrange in a shallow baking pan. Roast for 10 to 15 minutes or until brown.
Meanwhile, discard the vegetables from the roasting pan. Pour the pan drippings into a 4-cup measure. When the fat separates and rises to the surface, spoon 1/3 cup of it into a medium saucepan; discard any remaining fat. Squeeze the juice from 12 of the orange wedges into the defatted broth; if necessary, add water or chicken broth to make 4 cups. Whisk the flour into the fat in the saucepan and cook over medium heat, stirring constantly, for 3 minutes. Add the broth mixture and cook, stirring constantly, until the gravy thickens and boils, 5 to 7 minutes.
Arrange the remaining baked oranges with the sage on the platter around the turkey. Serve with the gravy.