Roughly chop the red onion and gently fry in a spoonful of oil. Peel, trim and grate the butternut and add it to the pan. Cook, stirring, for a few minutes. Add the veggie stock and chopped sage leaves. Simmer for about ten minutes or until all is soft. Add a pinch of salt and freshly ground pepper to taste. Whizz until smooth in a blender. Serve on your choice of pasta and vegetables.