Place the first three ingredients in a small saucepan. Bring to a boil. Reduce heat; cover and simmer for 4-5 minutes or until vegetables are crisp-tender. Drain and keep warm. In another small saucepan, melt butter. Stir in flour. Gradually stir in milk. Bring to a boil; cook and stir for 1 minute or until thickened. Reduce heat. Add American and Parmesan cheeses; cook and stir until cheeses are melted. Pour over vegetables and serve with additional Parmesan cheese if desired.