Preheat the oven to 250°F. Trim the duck breasts and score the skin side. Season with salt and pepper. In a large ovenproof skillet over medium heat, heat the oil. Cook the duck breasts, skin side up, for 2 minutes, then turn and cook for 5 minutes, or until still pink inside. Remove the skillet from the heat, turn the breasts over again, and place in the oven for up to 20 minutes while preparing the sauce.
To make the sauce: In a small saucepan, cook the stock or broth and sage over medium heat for 10 to 15 minutes, or until reduced to about 1 cup. Add the vinegar and cook for 1 minute. Add the dried cherries and cook for 3 to 5 minutes, or until tender. Add the green onion and cook for 30 seconds.
To serve, cut each duck breast into 10 to 12 slices and spoon the sauce over the top. Serve with a mixed salad or wilted spinach. Serves 6