Melt 2 tablespoons butter in medium sized stock pot, and sauté onion, garlic and celery until tender. Add broccoli and broth; cover and simmer for 10 minutes. Purée soup (I use a hand blender) or mash with potato masher. Return to heat. In small saucepan, over medium heat melt 3 tablespoons butter, stir in flour and add milk. Stir until thick and bubbly, add to soup. Add cheese; stir until melted. Season with pepper and serve.