Wash hands well with soap and warm water. Wash produce thoroughly.
Preheat the oven to 400°F. Line or grease a baking sheet.
Cut the butternut squash in half lengthwise and remove the seeds. Place on the baking sheet, brush with olive oil, and sprinkle with salt & pepper. Bake for 30-40 minutes, until tender. Remove from oven and let it cool slightly. Scoop out the flesh.
In a large pan over medium heat, sauté onion until soft, about 5 minutes. Add chopped sage and sauté for about another minute.
Add roasted squash, garlic and vegetable broth. Bring to a boil and then simmer for about 20-25 minutes. Cool slightly.
Pour into a blender, processing it in batches until smooth.
Pour back into the pot to keep it warm. Season with salt and pepper.