Heat the olive oil in a pan and fry the onions, carrots, celery and garlic until soft. Add the pumpkin and cook for 5 minutes, then tip in the stock and simmer until the pumpkin is soft and you can mash it with the back of a spoon. Add the cream and cook gently for 2-3 minutes. Put everything in a blender and whizz until smooth (or use a stick blender). Gently reheat to serve, grating over a little nutmeg, if you like.