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. Saute onion and carrots until slightly brown.
Stir in cooked butternut squash pulp, broth and 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: vegan sour cream (or dairy sour cream or plain yogurt), roasted pumpkin seeds, chopped cilantro, and/or chipotle sauce
Soup can be made and 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.