A classic roux is the thickening agent for this traditional Cajun-style gumbo made rich and hearty with chicken, sausage, onions, bell peppers, celery, garlic, and lively seasonings. Posted on September 7, 2021 by Caitlin Acosta A classic roux is the thickening agent for this traditional Cajun-style gumbo made rich and hearty with chicken, sausage, onions, bell peppers, celery, garlic, and lively seasonings. Advertisement