Place flour and salt into a bowl. Mix the rest of ingredients together and leave to stand for a good 10 minutes. Then make a well in the flour, pour in the liquid and whisk to a batter. Whisk very well in order to avoid lumps. The beer batter is best used after 15-20 minutes. (If the batter is too thick, you can add more liquid - sparkling water and Heineken).
Place the pollock into the flour, then into the batter and then fry at 180˚C.
Peel the potatoes and cut them into 1 cm square batons the length of the potato. Wash the starch off the potato with cold running water, place into a pan of slightly salted cold water and bring to a rapid boil. Chill them straight away in cold water to stop them cooking any further.
Dry them off well and plunge into the hot oil at 140˚C to blanch for 2-3 minutes, then drain. Heat the oil back up to 180˚C. Then plunge the chips back into the oil until they are golden brown (4-5 minutes), then season with sea salt.
You will only have problems with the frying if the oil is not hot enough as they will not colour properly or go crispy, then they may become soggy.
When we cook the chips three times they will take on some of the water when they are blanched which not only helps the fluffiness of the potato, but also helps the potato being crisp as opposed to soggy. As after the chip has been blanched for the first time they have started to cook from the inside. So when the chip hits the oil for the first time they are cooking instead of being blanched. So for the last fry they will be crispy.
Whisk the mustard, salt, pepper, and egg yolk in a bowl then slowly pour the oil on to the egg yolks whisking well, keep adding all the oil, you will need to add a little water to the mayonnaise as it may get to thick and split. Then once all the oil has been added place the rest of the ingredients into the mayonnaise. Tartar sauce is great with battered fish, as it cuts through the oily batter.