Pour the vegetable oil into your deep-fat fryer or a large frying pan and preheat it to 120°C. Cut the potatoes into 1cm thick slices and then across into 1cm wide chips. Fry in the preheated fryer for about 5 minutes until almost cooked, then drain them and put to one side. Turn the fryer up to 180°C.
To make your batter, place the flour in a mixing bowl and add the beer and the egg yolk and whisk together. In a separate bowl, whisk the egg white with a pinch of salt until it starts to form soft peaks. Carefully fold the egg white into the beer mixture until it’s just mixed in, making sure you don’t stir it too much.
Hold one of the haddock fillets by the very end of the tail and dip it into the batter. Let any excess drip off and then carefully place it into the hot oil. After a couple of minutes add half the chips and continue to fry for a further 5 minutes, or until golden brown, crispy and cooked through.
Drain, keep warm and repeat with the second fish fillet and the rest of the chips. Sprinkle with salt, drizzle with vinegar, and serve with some pickled eggs and gherkins. Delicious!