Preheat oven to 350 degrees F (175 degrees C). Place the squash halves cut side down in a baking dish. Bake 45 minutes, or until tender. Remove from heat, and cool slightly. Scoop the pulp from the skins. Discard skins.
Melt the butter in a skillet over medium heat, and saute the onion until tender.
In a blender or food processor, blend the squash pulp, onion, broth, brown sugar, cream cheese, pepper, and cinnamon until smooth. This may be done in several batches.
Transfer the soup to a pot over medium heat, and cook, stirring occasionally, until heated through. Garnish with parsley, and serve warm.