Toss the sweet potatoes, onion and garlic with the olive oil, rosemary, cinnamon, salt and pepper.
Spread into an even layer on a baking sheet.
Roast for 20 minutes, or until sweet potatoes are fork tender.
Remove from the oven and transfer to a large blender or food processor.
Add the vegetable broth and cream.I did this in two batches, because my blender and food processor were both too small to hold all of the soup. I placed half of the sweet potatoes, half of the broth and half of the cream in the blender and pureed, I then transferred the soup to a large bowl, then pureed the remaining sweet potatoes, broth and cream.
Once all of the soup has been pureed, pour into bowls and serve topped with sour cream or crème fraîche, if you’d like!