Step 1
Place a wire rack over a baking tray. Cook the chips in a large saucepan of boiling water for 10 mins or until just tender. Drain well. Arrange in a single layer on wire rack. Place in the fridge for 1 hour to chill.
Step 2
Add enough oil to a wok or large saucepan to come halfway up the side of the wok or pan. Heat to 130°C over medium-low heat (when oil is ready, a cube of bread turns golden brown in 30 secs). Cook the chips, in 4 batches, for 5 mins or until light golden and crisp. Transfer to a baking tray lined with paper towel. Place in the fridge to chill. Reserve oil in the wok or pan.
Step 3
Meanwhile, to make the yoghurt tartare, combine the yoghurt, capers, cornichons, shallot, dill, chives, tarragon, hot sauce, if using, and lemon juice in a medium bowl. Season. Place in the fridge until needed.
Step 4
Combine the combined flour and baking powder in a large bowl. Season. Add the beer, soda water and vinegar and stir until just combined. Place batter in the fridge for 30 mins to rest.
Step 5
While the batter is resting, place extra potatoes in a medium saucepan and cover with cold water. Bring to a boil over high heat. Reduce heat to medium and simmer for 10-15 mins or until potato is just tender. Drain well. Cool slightly. Cut into 1cm-thick slices.
Step 6
Reheat oil in the wok or pan to 180°C over medium heat (when oil is ready, a cube of bread turns golden brown in 15 secs). Dust the potato slices with a little flour. Dip into the batter, 1 at a time, allowing excess batter to drain. Carefully add to the hot oil and cook, in 3 batches, for 3 mins or until golden brown and potato is tender. Use a slotted spoon to transfer to a plate lined with paper towel. Sprinkle with chicken salt. Loosely cover with foil to keep warm.
Step 7
Dust the fish with a little flour. Dip into the batter, 1 at a time, allowing excess batter to drain. Carefully place the fish in the hot oil and cook, in 2 batches, for 5 mins or until golden brown and fish is just cooked through. Transfer to a wire rack over a baking tray lined with paper towel. Season.
Step 8
Cook the chips in the hot oil, in 3 batches, for 3 mins or until golden brown and crisp. Transfer to a plate lined with paper towel. Season with chicken salt.
Step 9
Arrange the potato cakes, chips and fish on a serving platter. Serve with yoghurt tartare and lemon wedges.