Remove the seeds from the pumpkin, peel it, and cut it into small pieces.
Slice the onion thinly.
Melt butter in a pot and sauté the onions.
Add the pumpkin and sauté together.
Pour in water or milk and bring to a boil.
When the ingredients are soft, blend until smooth.
Bring to a boil again, then season with salt and pepper.
Transfer to a bowl and serve.