In a separate large bowl, combine the flour, cornstarch, paprika, garlic powder, onion powder, dried thyme, dried oregano, salt, celery salt, black pepper, white pepper, baking powder, and cayenne pepper (if using). Mix well to create the seasoning mixture.
3/4 cup all-purpose flour, 1/4 cup cornstarch, 1/2 tablespoon smoked paprika, 1/2 tablespoon garlic powder, 1/2 tablespoon onion powder, 1/2 teaspoon dried thyme, 1/2 teaspoon dried oregano, 1 teaspoon salt, 1 teaspoon celery salt, 1 teaspoon black pepper, 2 teaspoon white pepper, 1/2 teaspoon cayenne pepper, 1 tablespoon baking powder