Preheat the oven to 180 °C (350 °F).
Thoroughly clean the ducks, then pat dry with paper towel. Trim excess skin from the ends, then place in a large, high-rimmed roasting pan. Generously season with salt, four peppercorn blend and rosemary.
Place the ducks in the oven, loosely cover with a sheet of aluminum foil and cook for 3 hours.
After 2 hours of cooking, remove from the oven and place the baby potatoes around the ducks. Roll the potatoes in the cooking juice so that they are thoroughly coated.
Slather the ducks with the peach syrup and return them to the oven, uncovered, for the last hour of cooking. When there is 30 minutes left of cooking, brush the top of the ducks once more with peach syrup and add the peach halves to the pan, arranged around the ducks.
Remove from the oven and let stand for 15 minutes before serving with oven-roasted Brussel sprouts.
