Peel, deseed and chop up the pumpkin into medium sized pieces.
Peel and finely dice the onion and the garlic.
Peel and finely grate the ginger.
Chop off the root end and the long skinny ends of the lemongrass (if they haven’t already been removed). With the tip of your knife, make a slit right down the stalks and then remove the tougher outer layers. Then bruise them with a rolling pin, a meat tenderiser or the spine of your knife. Finely slice them up and place them with the onion and the garlic.
Using a very big saucepan, over a medium heat, melt together the oil and the butter and as soon as they start to bubble add the onion, the ginger and the lemongrass and cook gently for 3 minutes, stirring often. (If they start to brown turn the heat down a little bit.)
Add the garlic and the curry paste and continue cooking for one more minute.
Remove it from the heat, add the pumpkin, and stir it all together.
Pour over the liquid stock or add cups of water mixed with the amount of dry stock recommended on the packet. (The stock should just cover the pumpkin by about 2 ½ cm).
Return the saucepan to the heat, turn it up to high and bring it to the boil (this will take a while). Once boiling, turn the heat down to medium/low or a temperature to where the soup is just simmering (softly boiling).
Simmer until the pumpkin can be pierced easily with a knife (around 30 minutes).
Meanwhile, get the food processor out of the cupboard and place a large colander (or a sievover a very large bowl.
When the pumpkin is cooked pour it out into the colander so that the pumpkin is sitting in the colander and the liquid has strained through into the bowl underneath.
Leave it to cool until it and the liquid is at a temperature that you are happy to place into the food processor.
Once cooled a little, place the pumpkin and 3 cups of the liquid (keep the remaining liquiinto the food processor and process it all until smooth. (You can use a blender but will need to do it in two parts.) (If you have a 'magic kitchen wand' you can return the pumpkin and the 3 cups of liquid to the saucepan and puree it. Then go on to add the coconut cream and the sugar, as below.)
Return the blended pumpkin back to the saucepan and add the coconut cream (leave aside 2 tablespoons for garnisand the sugar.
Add some of the remaining stock from the bowl until the soup is the thickness you prefer.
Over a medium/low heat, heat it through, stirring occasionally (preparing garnishes whilst you wait).
Just before serving garnish with some of, or all of these things; Finely diced spring onion, fresh coriander leaves (the more the better), chopped, roasted peanuts, finely sliced, fresh red chilli, swirls of the remaining coconut cream, also several drops of freshly squeezed lime juice.
Keeps covered in the fridge for up to 3 days and freezes well in containers for up to 3 months.