This dish is a Thai desert (a ‘khanom waan‘ in Thai). It is great and a favourite of mine.
Cooking the Pumpkin
To make this dish you need to simmer chunks of pumpkin in water with sugar in it for as long as it takes for nearly all the water to evaporate. My Thai wife reckons this should take around 1 hour if the heat is set at a low level. To start with the water should just cover the pumpkin. Use about half the amount of sugar to water when you are boiling the pumpkin: ie. 500 grams of sugar for 1 litre of water.
Preparing the Coconut Milk
When the pumpkin is cooked, simmer the coconut milk for 10 to 15 minutes. Add a small amount of salt when the water reaches boiling point and stir well before leaving to simmer. The salt in the coconut milk has the effect of intensifying the coconut taste and acting as contrast to the extreme sweetness of the pumpkin.
Finishing The Dish
Simply place the pumpkin pieces in a dish and add the salted coconut milk on top. My Thai wife tells me that the sweetened pumpkin keeps for several days if stored separately. Once the coconut milk is added it starts breaking down the pumpkin and cannot be kept for any length of time.