Prepare the frozen vegetables according to directions on package; drain and set aside.

In a large saucepan, melt butter or margarine; stir in flour, salt, and mustard. Cook over low heat, stirring constantly, until mixture is smooth and bubbly, about 4 minutes. Remove from heat. Stir in the milk and Worcestershire sauce.

Heat the milk mixture, stirring constantly, until it boils and thickens enough to coat a spoon, about 4 minutes. Stir in the cheese.

Cook and continue to stir over medium heat until the cheese is melted, about 5 minutes. Stir in the vegetables and beer, and bring the soup back to a simmer. Garnish with croutons.