Heat the oven to 425 degrees. Spread the squash in a nonstick 15x10x1-inch pan; drizzle with the oil. Sprinkle the squash with salt and pepper; stir to coat.
Roast for 25 to 30 minutes or until tender, stirring once.
Meanwhile, cook the bacon in a large Dutch oven over medium heat until crisp, stirring frequently. Add the onion, celery, garlic and pepper to the bacon. Cook for 5 to 7 minutes or until tender, stirring frequently.
Add the broth, cooked squash and all of the remaining ingredients except for the sour cream. Cook until thoroughly heated. Blend with an immersion blender, or place half of the mixture in a regular blender container. Cover and blend until smooth.
Pour the soup into a large bowl. Repeat with the remaining mixture. Return the soup to the Dutch oven and whisk in 1/2 cup of the sour cream.
Heat the soup over low heat until the desired temperature is reached. Garnish each serving with a dollop of sour cream.