Melt butter in a small Dutch oven over low heat; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add broth and milk; cook over medium heat, stirring constantly, until thickened and bubbly. Stir in pepper.
Add next 3 ingredients, and bring to a boil, stirring frequently. Remove from heat; add cheese, and stir until melted. Ladle soup into individual bowls. Garnish each serving with croutons, if desired. Serve immediately.