Rinse the duckling inside and out, removing the neck, heart, gizzard and liver. Place the “innards” in the bottom of a roasting pan.
Season the duckling with salt and pepper inside and out. Place onion pieces into the duck cavity. Squeeze juice from the orange over the duckling, then put rinds into duck cavity. With a thin knife, cut a slit on each side of the breast and in each leg/thigh, and insert the vanilla bean halves. Put duckling on top of “innards” in roasting pan.
Roast duckling for 15 minutes in a 500 degree oven, then lower oven to 350 degrees and roast until a thermometer inserted into the duckling registers 165 degrees. Remove from oven and allow to cool for 30 minutes.
Remove and discard onion and orange rinds. Using a cleaver, remove the back bone by standing the roasted duck on its neck end and cutting down each side of the back bone. Remove the rib cage and hip bones by slipping your finger tips around them, then lifting up and twisting the bones off the meat. The wing and leg bones remain.
Set innards aside and defat the roasting pan, then deglaze pan with the duck or chicken stock. Bring stock to a boil, adding bones and innards, and reduce stock to 1 cup. Remove the two half beans from the legs of the duckling and add to the cup of reduced stock, then reduce again to ½ cup.