First, roughly dice the pumpkin flesh. Peel and roughly cut the onion. Put both together with the butter in a saucepan and simmer for approx. 10 minutes over low heat until soft. Add the stock and let everything simmer for about 20-30 minutes, stirring occasionally.
Remove the saucepan from the plate and use a hand blender (alternatively a mixer) to chop it up.
Then push again on the plate, add the cream and let it boil again briefly.