Put 2 tablespoons of the curry paste into a large roasting tray or oven dish (approx. 25cm x 35cm) and gradually mix in the water to loosen. Pour in the coconut milk, add the fish sauce and a couple of pinches of salt, and stir to combine (don’t worry if the coconut milk is lumpy at this point, it will dissolve as it cooks), then mix in the rice.