Using a mortar and pestle, finely grind the coriander with all the other ingredients up to and including the salt, mix with the oil. Put a frying pan on the heat, rub the seasoned oil into the duck breasts, fry for approx. 5 mins. on each side. Remove the pan from the heat, cover and leave in the pan to rest for approx. 10 mins.
Gently melt the reserved fat in a pan to create approx. 3 tbsp of liquid fat. Remove the remaining skin. Add the shallots, chilli peppers, sugar and salt, simmer for approx. 4 mins.
Boil the potatoes (uncovered) in salted water for approx. 20 mins. until soft, drain and return to the pan, mash with a potato masher or fork, season, plate up with the duck breasts and shallot & chilli oil.