Use a heavy based pot or a wok and heat it on medium heat. Add the oil and the spice paste. Saute until the garlic and the ginger leave out their aroma.
Toss in the chopped onion and the sugar, cook until the onions are translucent and start to caramelize.
Add the chicken thighs and mix well making sure that the chicken is well coated with the spice mix.
Pour the vinegar, soy sauce and the chicken stock in a measuring jug and add altogether on to the chicken thighs. Also put in the bay leaves. Cover the lid.
First bring to boil over medium-high heat and then reduce heat to let simmer for about an hour, until the meat is tender and the stock has reduced.
Check internal temperature of chicken thighs to reach 74° Celsius (165° F).
Once the sauce is reduced it will have a sticky caramel texture.
The sauce is tasty any way. If you want it to caramelize turn the heat higher to reduce the sauce.
Serve warm.