1: To make thick chips, top and tail each potato, then use an apple corer to cut out the centres. Remember, we are making round chips here. Bring a large saucepan of salted water to the boil over a high heat. Add the potatoes, return the water to the boil and boil for about 5 minutes until tender, but still holding their shapes.
2: Use a slotted spoon to remove them from the water and leave them to drain. Dry well on a wire rack.
3: When the potatoes are completely dry, heat enough oil for deep-frying in a deep-fat fryer or heavy-based saucepan until it reaches 140°C. Add the potatoes and fry for 8–10 minutes until the oil stops bubbling, which means all the moisture has been removed. Use a slotted spoon to remove the potatoes from the oil, return them to the wire rack and leave to cool completely.
4: Meanwhile, make the tartare sauce. Place the egg yolks, Dijon mustard and white wine vinegar in a food processor and blend until smooth. With the motor still running, slowly add the oil until the mixture emulsifies and thickens. Stir in the remaining ingredients and season. Cover and keep in the fridge until needed.
5: To make the pea purée, melt the butter in a saucepan over a low heat. Add the shallots and sea salt and fry, stirring occasionally, for at least 5 minutes until softened, but not coloured. Add the chicken stock and mint and bring to the boil. Add the peas and sugar, return the stock to the boil and boil for 5–6 minutes until the peas are tender. Strain the peas and shallots over a bowl to catch the liquid, then transfer them to a blender.
6: Add 2 tablespoons of the cooking liquid and blend until smooth, but not too thin. Adjust the seasoning with table salt, if necessary, then set aside and keep hot.
7: To make the batter, mix the egg whites and beer together until fluffy. Mix the flour and bicarbonate of soda together in a large bowl and add the egg-white mix.
8: Just before you are ready to fry the fish, fry the potatoes for a second time. Reheat the oil to 180°C. Add the potatoes to the fryer again and fry for 2–3 minutes until crispy and golden brown. Drain well on kitchen paper, sprinkle with salt and keep hot in a low oven.
9: Reheat the oil to 180°C, if necessary. Dip the fish into the batter, letting any excess drip back into the bowl, then add to the oil and fry for 3–5 minutes until crispy and golden brown. Drain on kitchen paper. Keep the fried fillets warm in the low oven until they are all fried, but do not cover them with kitchen paper.
10: Sprinkle with sea salt flakes and serve immediately with the chips, pea purée and tartare sauce and lemon wedges for squeezing over.