In a large dutch oven, sweat down celery, bell pepper, onion and garlic for about 5-7 minutes in butter. Added sliced andouille sausage and brown for another 5 minutes.
Stir in diced tomatoes and Cajun seasoning. Pour in chicken broth, water then add in chicken. Season with salt and pepper and add bay leaf. Let simmer for a minimum of 30 minutes. You can let this sit all day if you like, the longer the more the flavors will marry together.
15 minutes prior to serving, add in shrimp and let the soup continue to simmer. Serve with sliced scallions and enjoy!