Nutmeg, cinnamon, and maple syrup season the leeks and sweet potatoes in this thick and creamy side-dish soup.
In a 4-quart Dutch oven cook onion, celery, leek or green onion, and garlic in hot butter until onion is tender but not brown.
Add sweet potato, broth, cinnamon, and nutmeg; bring to boiling. Reduce heat and simmer, covered, 20 minutes or until potato is tender. Remove from heat; cool slightly. Remove cinnamon and discard.
Transfer mixture, about 1/3 at a time, to blender container or food processor bowl. Cover and blend or process till smooth. Return all soup to the Dutch oven. Stir in half-and-half and maple syrup; heat through.
To serve, garnish with celery leaves.