Preheat the oven to 375 degrees F. Place the milk and flour in a medium-sized pot and whisk to combine; set over medium heat and bring to a gentle simmer. Whisk in 3/4 of the cheese, add the paprika, cayenne, salt and white pepper. Reserve the sauce over low heat. Arrange the fish in a lightly buttered 9" x 13" baking dish. Pour the cheese sauce over it; sprinkle each piece with an equal amount of the remaining cheese and the breadcrumbs. Bake, uncovered, for 15 minutes, or until the fish is golden on top and cooked through.