Heat your oven to 190°C/Fan 170°C/Gas 5. Pat the duck legs dry with kitchen paper. Prick them all over with a skewer or fork (this will help make the skin crispy). Rub a little salt and pepper into the skin. Dust ½ tsp China 5 spice over each leg. Lay the duck legs, skin-side up, on a wire rack in a roasting tin. Roast for 1 hr till golden and crisp.
When the duck is 20 mins from being ready, tip the rice into a bowl. Cover with cold water. Whisk for 1-2 mins till the water is cloudy (this is the starch). Drain and rinse. Tip into a small pan. Add 400ml boiling water and a pinch of salt. Cover.
Bring the rice to the boil, then turn the heat right down and very gently cook for 8 mins till all the water is absorbed. Take off the heat and leave to keep warm in the pan.
While the rice cooks, tip the blueberries into a small pan. Slice 1 cm off the thumb of ginger. Peel and grate it. Add it to the pan. Add 1 tbsp of the vinegar.
Add 1 star anise to the pan. Pour in 1 tbsp tamari and the honey. Set the pan over a medium heat. Gently cook for 10 mins, stirring now and then, till the blueberries break down and form a sauce. Take off the heat. Taste and add more tamari or vinegar if you think it needs it. Put on the lid on to keep it warm.
The duck legs should be golden and crisp. Arrange them on warm plates and serve them with the rice, handfuls of watercress and the warm blueberry sauce.