Mix the rub ingredients together and then coat the chicken with it. Leave for at least an hour
Next, roughly chop the ingredients for the spice paste then blend to a paste
Get your BBQ lit. You want a nice gentle fire in order to grill the chicken directly over the coals. Alternatively, heat an over to 190c
In a frying pan, heat the oil and fry the spice paste along with the tamarind and the tops of the lemongrass stalks for 5 minutes. Add the water and cook for a further 5 minutes
Add the coconut milk, sugar & salt then let it simmer for 5 minutes
Grill the chicken over the coals, turning frequently and basting with the sauce you've just made. Keep on building layers of the sauce on the chicken as much as possible. The chicken should be done after 20-30 minutes but please check with an instant read thermometer. You are aiming for 74c internal temp
If using an oven, roast for 30 minutes, basting every 10 minutes. I'd highly recommend using a BBQ though if you have one!