Peel the pumpkin. Since it is very difficult to peel, I put it in a kettle with boiling water for 3-4 minutes. Then let it cool down, cut open and remove the core. Cut the rest into small pieces and puree in a blender with the onions roasted in butter, the garlic clove and the finely chopped lemongrass. Add a little water.
Put the chicken stock and pumpkin mixture in a saucepan and simmer until the soup is creamy. Add coconut milk and bring to the boil again. If necessary, add a little more broth. Finally add the prawns and let them steep.