Preheat the oven to 375 degrees. Cut the squash or pumpkins in half and remove the loose stringy membrane and seeds. Place the squash cut side down on a greased baking sheet, and roast in the oven until tender (about 40 minutes). Let the squash cool, then remove the peels. Place the squash in a food processor or blender, and process until smooth. This will yield approximately 4 1/2 cups of mashed squash.
In a large pot, saute the onion and celery in the olive oil over medium low heat until tender. Add the garlic and saute for another 30 seconds.
Add the roasted squash, broth, and maple syrup. Then add the cinnamon, cumin, ginger, and cayenne pepper (if using). Stir everything together, then simmer for 20 to 30 minutes, until thickened to your liking.
Taste the soup and add the teaspoon of salt (or more) if needed. Adjust the other seasonings as needed.
Use an immersion blender to make a smooth pureed soup. If you don’t have an immersion blender, use a regular blender or food processor to puree the soup in small batches.