On a baking sheet, arrange the butternut squash, halved garlic head, and rosemary. Drizzle generously with avocado, and season with salt and freshly cracked black pepper. Roast on the middle rack of the oven for 40-50 minutes, or until the squash is tender.
Once done, set the garlic aside and transfer the remaining vegetables to a blender. When the garlic is cool enough to handle, squeeze the roasted garlic cloves into the blender, discarding the skins.
Add maple syrup and 4 cups of vegetable/chicken broth to the blender. Blend until smooth. Transfer the soup to a medium saucepan and bring it to a gentle boil over medium heat. Reduce to a simmer, adjusting seasoning with salt and pepper. Add more broth if needed to reach your desired consistency. Serve hot, garnished with extra black pepper.