Preheat oven to 350F/176C degrees. Wash outside of squash, pierce with knife in 3-4 places, place on baking sheet and roast whole for about 90 minutes, or until knife easily slides in. Remove from oven and set aside to cool.
After squash has cooled enough to handle, cut down the middle, carefully scoop out seeds, then scoop out all the pulp. At this point, the squash pulp can be tightly covered in a container and placed in the refrigerator for a few hours or days, until you are ready to use it.
Put olive oil in large heavy bottomed pot over medium high heat. Sauté 1 medium diced onion and 2 medium diced carrots until slightly brown.
Stir in cooked butternut squash pulp, 6 cups broth and 1 tablespoon chipotle sauce (can add more than 1 tablespoon if want soup spicier). Heat the soup to a boil, then reduce heat and simmer uncovered for 15-20 minutes.
Remove from heat and use an immersion blender to puree the soup until smooth. Season with salt and pepper to taste.
Top with optional accompaniments: sour cream (or plain yogurt), roasted pumpkin seeds, chopped cilantro, and/or chipotle sauce
Soup can be frozen for up to 3 months. Thaw in the refrigerator for a day before using.
Blend the soup again before heating to get a smoother consistently, if needed.
How to roast pumpkin seeds for the soup:
Place raw (green hulled) pumpkin seeds on an ungreased baking sheet and roast for about 4-5 minutes in a preheated 400F/204C degree oven.