Spray 4-quart Dutch oven or large saucepan with cooking spray; heat over medium heat. Add onion and garlic; cook until tender. Add flour; cook and stir over low heat 1 to 2 minutes.

Add chicken broth; bring to a boil. Add broccoli and potatoes; reduce heat and simmer, covered, about 15 minutes or until vegetables are tender. Remove and reserve 1-1/2 cups broccoli mixture with slotted spoon.

Process remaining broccoli mixture in batches in food processor or blender until smooth; return to Dutch oven. Stir in reserved broccoli mixture and milk. Cook over medium heat until heated through. Remove from heat; stir in cheese until melted. Stir in salt and pepper. Sprinkle with ground nutmeg, if desired.