Preheat your deep fryer to 375 degrees F.
Combine the flour, cornstarch, baking powder, salt and white pepper in a bowl. Pour the beer into a second bowl. Add the flour mixture and whisk until a smooth batter forms.
Dip the fish in the batter and deep-fry 5 to 6 minutes, turning once, or until richly coloured and crispy. Drain the fish well and serve.