2. Meanwhile, heat the oil in a large soup pot over medium heat. Add the onion, celery and apples, and cook until soft and translucent, about 5 minutes.
3. Season lightly with salt and pepper, add the cumin and curry powder and cook for 2 more minutes.
4. Remove the seeds from the squash and discard them. Scoop the squash pulp out of the skin with a spoon and add it to the soup pot along with the sherry or white wine and cook for 2 or 3 minutes more.
5. Puree this mixture in a blender in batches, being careful not to overfill the blender and adding broth as needed.
6. Reheat the soup and add the remaining broth to adjust the consistency. Season with salt and pepper.
7. Serve the soup in warm bowls with a dollop of sour cream.