1. Bring vinegar to a boil in a small saucepan. Reduce heat; simmer over medium heat about 15 minutes or until reduced to 1/4 cup. Mix butter and flour in small bowl until smooth. Stir broth and pepper into vinegar. Gradually whisk in butter mixture until sauce is smooth; bring to a boil. Reduce heat; simmer 3 minutes, stirring constantly. Serve immediately.