Pat the fish completely dry with kitchen paper.
Mix the 150g plain flour, cornflour, baking powder and salt in a large bowl.
Gradually whisk in the very cold beer until you have a smooth batter with the consistency of thick cream. Do not overmix.
Heat the oil to 175°C to 180°C / 350°F to 355°F.
Place the extra flour on a plate. Lightly coat each fillet and shake off any excess.
Dip each fillet into the batter until completely coated.
Carefully lower the fish into the hot oil. Fry in batches so the pan is not overcrowded.
Fry for approximately 5 to 7 minutes, depending on thickness, until crisp and golden and the fish is cooked through.
Remove and drain on a wire rack. Season lightly with salt.
Serve immediately with homemade chips, vinegar and tartare sauce or garlic mayo.
If frying in batches or finishing your chips afterwards, heat the oven to 100°C conventional / 80°C fan / 210°F.
Place the cooked fish on a wire rack set over a baking tray and keep it uncovered in the oven for no longer than about 10 to 15 minutes.
Do not cover with foil, as trapped steam can soften the batter.
