Place the vinegar, coriander seeds, peppercorns, sugar, 1 teaspoon of salt, and 150ml water in a saucepan over a medium heat.
Stir until the sugar has dissolved.
Scoop the onions into a bowl, then carefully pour over the hot pickling liquid.
Leave to cool for 15 minutes, then cover, and chill for at least 1 hour. Will keep chilled for up to 2 days.
Combine the mayonnaise, dill, basil, mustard, and capers in a bowl, then cover, and chill. Will keep chills for up to 2 days.
Sift the flour and cornflour into a bowl, then stir through the salt.
Make a well in the centre, then whisk in the cold beer to make a smooth batter.
Cover the batter, then chill for 30 minutes.
Heat the oil in a deep, heavy-based pan, no more than two thirds full, until the oil reaches 190°C on a cooking thermometer. Alternatively, you can check the oil is ready by dropping a small cube of bread into the oil.
It should turn brown in about 10 seconds.
Dip each piece of cod into the batter until fully coated, then gently shake off the excess.
Fry the fish in batches for 4 minutes per batch, then remove using a slotted spoon and drain on kitchen paper.
Warm the tortillas in a low oven or dry frying pan.
Spread the tartar sauce over the tortillas, then add the fish.
Top with the pickled onions, shredded lettuce, and a dash of hot sauce.
4 servings