For the fish patties:

1. Remove the skin from potatoes and boil for 25 minutes. Drain, place in a large bowl, and mash cooked potatoes with a masher until smooth. Set to the side.
2. Heat a cooking pan at medium heat. Add the olive oil, chopped green bell peppers, onions, and celery, cooking for 5 minutes.
3. Season the flounder fish with 3 tablespoons of Creole seasoning, then place the fish on top of the onions and peppers, cooking for an additional 2 minutes on each side. Remove from heat.
4. Add cooked fish, onions, and pepper into a food processor (paid link) and blend, leaving the fish slightly chunky.
5. Add flour, 1 tablespoon Creole seasoning, and Panko breadcrumbs in a separate large bowl. Mix well.
6. Add the fish mixture and egg into the bowl with the mashed potatoes. Fold to combine ingredients.
7. Add onion powder, garlic powder, red cayenne pepper, basil flakes, paprika, sea salt, and black pepper fish mixture, then stir together until blended well.
8. Form palm-sized patties from fish mixture, then coat with breadcrumb mixture.
9. Heat a cooking pan at medium heat and add 1 inch of cooking oil. Pan-fry fish patties for 3 minutes per side. Remove from pan and place on paper towel to drain excess oil.

For the Pontchartrain sauce: 

1. Heat a cooking pan at medium heat. Add butter, garlic, and flour, stirring together until the butter melts. Add onion and celery. Cook for 2 to 3 minutes, then slightly lower heat. Add kosher seafood stock and stir until it begins to bind.
2. Add heavy cream, hot sauce, lemon juice, ground cumin, coriander, turmeric, ground allspice, nutmeg, ginger, harissa, sea salt, and black pepper to the pan and occasionally stir until blended. Remove from heat. Stir in grated Parmesan cheese until combined.
3. Serve sauce over fish patties.