In large saucepan, melt butter over medium heat; cook leeks and onion, stiring often, until softened, 5 minutes.
Add flour cook, stirring, just until starting to brown, about 2 minutes. Slowly stir in broth, water, ale and salt; bring to simmer.
Reduce heat to low; cover and simmer for 30 minutes.
Stir in cream; bring just to boil over medium heat. Add cheese, mustard, Worcestershire sauce and pepper; reduce heat to low. Stir until poping hot and cheese is melted.
Makes 8 serverings.