In large saucepan combine potatoes and broth. Bring to boiling; reduce heat. Simmer, covered, for 8 minutes. Mash slightly. Add broccoli and milk; bring just to simmering.
In a medium bowl toss flour with the 2 cups cheese; gradually add to soup, stirring cheese until melted. Season to taste with pepper. Ladle soup into shallow serving bowls. Top with greens and additional cheese.