Meanwhile, melt butter in medium saucepan on medium heat. Add onions; cook and stir 3 min., adding garlic for the last minute. Add flour; cook and stir 1 min. Gradually add broth; cook 5 min. or until thickened, stirring constantly. Add shredded cheese, 2 Tbsp. Parmesan and cayenne pepper; cook and stir 1 min. or until shredded cheese is melted. Remove from heat.