Preheat oven to 350℉.
In a large Dutch oven melt butter over medium heat.
Add onions and saute until tender.
In the meantime, season fish with Cajun seasoning and placed on baking pan. Bake at 350 until fish can be easily flaked with a fork. Remove from oven and using the fork, break up the fish into bite size pieces, set aside.
To the Dutch oven, add chicken broth, celery, carrots, and potatoes. Cook until vegetables are tender.
In a small bowl whisk together the milk, cake flour, celery salt and white pepper. Mix into the broth mixture. Stir constantly until thickened.
Add cheese to the soup mixture and stir until the cheese has completely melted.
Add the fish, stirring to combine. Serve with crackers, if desired.
Top with sliced crumbled bacon, green onion, chopped tomates and grated Cheddar cheese, if desired.
