Melt butter. Saute bacon, then add onion, leek, and celery. Cook until heated through. Add flour and stir until well combined. Stir in stock; simmer for 15 minutes. Add broccoli; simmer for 15 minutes. Pour into blender and puree. Return to pan and season with salt, pepper, and nutmeg. Stir in cream and cook until heated, do not boil.
Serve topped with cheese, if desired.