- Rinse the potatoes to get rid of any excess starch then put into a pan of cold salted water. Bring to the boil and cook for 2-3 minutes. Drain and return to the pan, then toss lightly to fluff up the edges.
- Fill a large pan ⅔ full with oil and heat to 160°C (or when a cube of bread browns in 60 seconds). Cook the chips for 6-7 minutes then remove and drain on paper towel in a single layer.
- For the mushy peas, tip the peas into a pan with a squeeze of lemon juice and butter. Heat up and mash the peas. Season well, then cover and set aside.
- Sift the flour, cornflour and 1 tsp salt into a bowl. Make a well in the centre and add the light ale. Stir with a wooden spoon until you have a smooth batter. Lightly beat the eggwhite until it's slightly foaming then fold into the batter.
- Bring the oil in the pan up to 190°C (or until a cube of bread browns in 20 seconds). Return the chips to the oil and fry for a further 4-5 minutes until golden and crisp. Remove and drain on paper towel. Tip into a warm bowl, season with sea salt and keep warm.
- Dust the fish in flour before you dip in the batter. Fry for 6-8 minutes, in batches, until golden and crisp. Drain on paper towel and serve with the chips and mushy peas.