When you are ready to eat, preheat the oven to 200C/400F.
If you haven’t already, place the marinated chicken (sauce and all) in a baking dish. I used a 28cm oval Le Creuset dish. Place the dish on a baking tray to catch any errant sauce and into the oven for 20-30 minutes, depending on the size of your chicken thighs and whether or not you are scared of undercooking chicken like me lol.
When the chicken is cooked through remove the dish from the oven, remove the chicken from the sauce and place the chicken on a plate to set aside.
In a small bowl, mix together the cornstarch or glutinous rice flour and water to form a slurry. Pour the slurry into the sauce mixture and stir to combine.
Return the dish (with just the sauce) to the oven for 5 or so minutes. It should be bubbling away and have thickened nicely.
When you are happy with the sauce, remove it from the oven. Place the chicken back into the dish and coat with the glossy, thick sauce. Serve immediately.
Leftovers keep well in the fridge and can be frozen and defrosted. The sauce can turn a bit jelly-like when cooled but it will loosen up when reheated.