4 x 175 g pieces of thick cod fillet (or any firm fresh sea fish) cut from the head end, not the tail
240 g plain flour
1 tsp salt
3 ½ tsp. baking powder
270 ml (9 fl oz) ice-cold water 900 g floury potatoes, such as Maris Piper
Sunflower oil, for deep-frying
Sea Salt and freshly ground black pepper
For the tartar sauce:
1 tsp finely chopped green olives
1 tsp finely chopped gherkins
1 tsp finely chopped capers
2 tsp chopped chives
2 tsp chopped parsley
Good quality mayonnaise
To make the batter, mix the flour, 1 tsp of salt and the baking powder with the water. Keep cold and use within 20 minutes of making.
Pre-heat the oven to 150ºC. Line a baking tray with plenty of kitchen paper and set aside.
Peel the potatoes and cut them lengthways into chips 1 cm (1/2 inch) thick. Pour some sunflower oil into a large deep pan until it is about a third full and heat it to 130ºC (260ºF). Drop half the chips into a frying basket and cook them for about 5 minutes, until tender when pierced with the tip of a knife but not colored. Lift them out and drain off the excess oil. Repeat with the rest of the chips and set aside.
To fry the fish, heat the oil to 160ºC. Season the fish fillets with salt and pepper and then dip into the batter. Fry, 2 pieces at a time, for 7 – 8 minutes, until crisp and golden brown. Lift out and drain on the paper-lined tray. Keep hot in the oven while you cook the other 2 pieces.
Raise the temperature of the oil to 190ºC and cook the chips in small batches for about 2 minutes, until they are crisp and golden. Lift them out of the pan and given them a shake to remove the excess oil, then drain on kitchen paper and keep them hot while you cook the rest. Sprinkle with salt and serve them with the deep-fried cod and tartare sauce.