Preheat the oven to 180°C / 350°F / gas 4. Carefully slice the duck breasts so that you can open them flat and place them on a piece of tinfoil and lightly season them. Melt the butter in the frying pan and saute all the stuffing ingredients, except the orange juice. When the stuffing looks done, add the juice and check the seasoning. Place the stuffing on one half of each duck breast and fold over. Wrap each one in tinfoil and bake for 40 minutes in the oven. Open each package carefully onto a hot plate so as not to lose the juices.