Begin by placing the chicken thigh fillets between two sheets of plastic wrap and pound them to about 0.7cm (1/3 inch) thickness using a meat mallet. Sprinkle both sides with cooking salt for flavor, then dust lightly with cornflour.

In a mixing bowl, combine cornflour, plain flour, baking powder, and a pinch of salt. Refrigerate this mixture for about 30 minutes to chill. Whisk in cold soda water until the batter is smooth and slightly frothy.

In a heavy-based pot, pour enough vegetable or canola oil to reach a depth of approximately 4cm (1.6 inches). Heat the oil to 160°C (320°F) over medium heat.

Dip each chicken cutlet into the chilled batter, ensuring it's fully coated. Fry for about 3 minutes until pale golden, then drain on paper towels for 20 minutes to firm up before the second fry.

In a small saucepan, add a splash of chicken stock with a teaspoon of cornflour, stir until smooth, then incorporate remaining stock, lemon juice, sugar, garlic, ginger, and optional cooking wine. Simmer until thickened.

Increase the oil temperature to 200°C (390°F). Fry the chicken cutlets in small batches for another 3 minutes until golden brown and super crispy.

Transfer the chicken to paper towels to absorb excess oil. Slice the crispy chicken cutlets, drizzle with lemon sauce, and garnish with lemon slices and green onions.