Simmer the squash in water for 10-15 minutes until soft. Drain and set aside.
Heat the olive oil in a large casserole over a medium high heat. Add the onions and chilli and saute until slightly soft. Add the reserved squash and the garlic. Saute gently until caramalised (20-30 mins), stirring occasionally.
Add the stock, orange juice, star anise and tarragon then bring to the boil and season with salt and pepper. Simmer for 30 minutes so that all the flavours can meld.
Now you can either push the soup through a sieve or remove the star anise and blend in a blender. Check seasoning and serve hot in soup bowls with a dollop of sour cream in each serving.