British
Cut potatoes into thick chips, rinse and pat dry, then soak in cold water for 10 minutes and drain well.
Heat oil to 140 C and blanch the chips for 5 to 6 minutes until soft but pale, then lift out and drain.
Whisk flour, cornstarch, baking powder and a pinch of salt, then whisk in the cold sparkling water to a smooth batter.
Raise the oil to 190 C. Fry the chips again for 3 to 4 minutes until golden and crisp, drain and salt.
Pat the fish dry, dust lightly with flour, dip into the batter and let excess drip off.
Fry the fish at 180 C for 6 to 8 minutes until deep golden and crisp, turning once.
Drain on a rack, season with salt and serve hot with the chips and malt vinegar.