Preheat the oven to 200°C.
Using one tablespoon of the olive oil, grease the sliced surface of the squash and season with salt and pepper, to taste. Arrange on a baking sheet and roast until very tender, about 45 minutes. Remove from the oven and let cool.
In a large heavy pot over medium-high heat, add the remaining olive oil, onion, celery, and carrot, then season with a pinch of salt. Saute until just tender, about ten minutes. Add the garlic and saute for two minutes. Scoop the butternut squash flesh into the pot and stir. Add 900 ml of the chicken stock and bring to a boil. Reduce the heat to low, cover the pot, and simmer until the vegetables are very tender, about 30 minutes.
Turn off the heat and using an immersion blender, carefully puree the soup until very smooth. If necessary, add more of the remaining stock to create desired consistency. Mix in two teaspoons of the chipotle into the soup, and season with salt and pepper, to taste.
In a small bowl, mix together one teaspoon of chipotle and the sour cream. Season the chipotle cream with salt and pepper, to taste. Transfer the soup to bowls. Top each with a dollop of chipotle cream and serve.
Cook's Notes: Serve this hearty bisque for dinner on a cool autumn night, or pour it into individual shot glasses for a savvy appetiser.