Preheat the oven to 350F. Heat a large frying pan over a moderate heat. Add the duck breasts, skin side down, and cook until the skin is browned and crisped, 2-3 minutes. Transfer the duck breasts to a roasting pan and place in the oven. Roast for 15 minutes for rare meat, 20 minutes for medium, and 25 minutes for well-done. With a sharp knife cut away the zest, pith, and skin from the oranges. Slide the knife down one side of a segment, cutting it from the skin. Cut down the other side and pull out the section. Repeat to remove the remaining segments. Place the orange segments, their juice, and the Grand Marnier in a medium saucepan and heat gently. In a small saucepan heat the sugar with 1/3 cup water, stirring until the sugar dissolves. Once the liquid is clear, raise the temperature and boil hard until it caramelizes. Once the caramel is a medium golden brown color, remove the pan from the heat and very carefully pour the vinegar into the saucepan. Pour off any fat from the frying pan where the duck breasts were fried and discard. Stir the orange mixture and caramel mixture into the pan and cook over low heat, scraping the bottom of the pan with a wooden spoon to loosen any attached particles. Remove the pan from the heat and beat in the butter, a little at a time, whisking after each addition. Spoon the sauce over the duck breasts before serving. Serve with apples sautÄed in butter or corn flans.
