In a large saucepan, melt butter over medium heat. Stir in flour until blended; gradually whisk in beer until smooth. Whisk in stock, Worcestershire sauce, mustard, salt, pepper and cayenne., Bring to a boil, stirring constantly; cook and stir until thickened, 1-2 minutes. Reduce heat. Gradually stir in cheese until melted. If desired, serve soup in bread bowls and top with crumbled bacon and shredded cheese.