Finely slice the onion, carrots, mushrooms and beans.
Finely chop the garlic and ginger.
Peel the sweet potatoes and roughly chop them. Put them into a saucepan of water, bring to the boil and gently cook for 15 minutes until tender. Drain, then return the sweet potatoes to the pan and add the other ingredients.Using a potato masher or stick blender, purée it until you get a slightly textured mash. Taste it, adjust the seasoning to your liking, then cover and set aside.
Meanwhile heat 1 Tbsp of duck fat in a shallow fraying pan or wok and gently fry the onion, garlic and ginger until soft. Add the carrots, put the lid on and cook for 5 minutes over low heat. Add the mushrooms, five spice, soy sauce and rice wine. Stir, and let it bubble for a few seconds, then cover and cook for 5 minutes.
Add the green beans and cook for a further 5 minutes.
Turn off the heat and add I small handful of coriander leaves (roughly chopped) and the sliced spring onions. Gently combine with the shredded duck meat then rest.
Turn on the oven, setting the temperature to 200°C or to the grill.
Spoon the duck mixture into a deep baking dish or several ramekins and top with the mash evenly (the mash should be about 2cm deep). Scatter some sesame seeds on the top, of used.
Put the dish(es) into the oven and bake for approx. 20-25 minutes until the top is golden.
Serve warm.