Put the knob of butter with some salt and pepper in a saucepan to melt. Add the onion and fry on a low heat for about 5 minutes until soft.
Add the sage and fry before adding the pumpkin and stock. Put the lid on and leave to cook on a low heat for about half an hour.
Blitz the soup with a hand blender until smooth, then add the cream and wine and stir. Taste and season again if needed. Try not to let the soup boil now. If the soup has a slight bitter taste from the wine, add a teaspoon of agave syrup or sugar to sweeten.