Heat up a pressure cooker with the oil.
Render the fat from the duck neck and back.
Caramelized the rest of the duck pieces, but don't cook the duck completely. Remove and set aside.
Fry the yam pieces till brown and set aside.
Remove the oil save 2 tablespoons.
Return the duck pieces and the yam pieces to the pressure pot.
Add all the sauce ingredients to the pot.
Cover and cook under pressure for 20 minutes.
Serve hot with steamed rice and a stir fried greens. Serves 6.