In a small bowl stir together all ingredients. Refrigerate until ready to use.
Preheat oven to 350 degrees F. Lightly spray baking sheet with olive oil cooking spray; set aside.
Cut catfish into 4-ounce serving portions. Place in a large zip-top bag; set aside.
In a small bowl stir together buttermilk and Cajun seasoning. Pour into zip-top bag over fish. Squeeze out air and seal. Marinate in refrigerator for 30 minutes.
Spread cornflake crumbs in a pie plate or shallow bowl. Remove fish from bag, shaking off any excess buttermilk. Coat catfish with crumbs and place on prepared baking sheet. Serve fish hot with tartar sauce.
Lightly spray with cooking oil and bake for 15 minutes.
For Creole tartar sauce: In a small bowl stir together all ingredients. Refrigerate until ready to use.