Onion and Sage Turkey Gravy   Ingredients: 6 tablespoons (3/4 stick) unsalted butter 1 large red onion, halved and sliced 1/4 inch thick 4 large garlic cloves, peeled and halved 6 tablespoons all-purpose flour Neck and giblets from your turkey (discard the liver) 4 cups good chicken stock, preferably homemade 2 tablespoons cognac or