Gather the ingredients. Preheat the oven to 400 degrees F (200 degrees C). Rinse flounder fillets and pat dry with paper towels. Lightly grease a shallow baking dish.

Combine crabmeat, crushed saltines, bell pepper, mustard, Worcestershire sauce, salt, and white pepper together in a medium bowl. Combine egg white and 1 tablespoon mayonnaise in a small bowl; stir into crabmeat mixture.

Brush fillets with melted butter; place in the prepared baking dish. Spoon crabmeat mixture over fillets and drizzle with any remaining butter. Bake in the preheated oven for 15 minutes.

Meanwhile, make topping: lightly beat egg yolk in a small bowl. Stir in 5 tablespoons of mayonnaise. Remove fish from the oven and spread this mixture over stuffing; sprinkle with parsley and paprika.

Increase oven temperature to 450 degrees F (230 degrees C) and bake until golden and bubbly, about 5 or 6 minutes.