Serve with a generous swirl of chive crème fraîche.
Peel and cut the butternut square into small piece. In a saucepan bring the water and chickens tock to a boil and add the butternut squash. Add salt and cook for 40 minutes or until the squash very soft. Keep a small amount of cooked squash to the side for a garnish at the time of serving. Using an immersion blender or hand blender purée the squash until the mixture is smooth and creamy. Add white pepper and heavy cream. Transfer back to saucepan and bring to simmer.
Mix together sour cream, buttermilk and salt. Chop the chives very finely and add to the mixture. Store overnight in the refrigerator for best results.
Portion into a deep soup plate, swirl in some chive crème fraîche and sprinkle ¼ of the reserved cooked squash in the middle. Garnish with a spring of fresh herbs.