1Place each chicken breast between two sheets of parchment paper or plastic wrap and pound with a meat mallet or rolling pin to an even thickness of about 1 cm (½ inch).
2Marinate the chicken fillets in pickle juice for at least one hour, ideally 5–6 hours for deeper flavor. Drain the juice and pat the meat dry with paper towels.
3In a large bowl, mix flour, powdered sugar, salt, pepper, and paprika. Set aside.
4In another bowl, beat the egg with milk until smooth.
5Dip each chicken fillet first into the egg-milk mixture, then into the flour mixture, pressing lightly to adhere. Shake off excess flour.
6Spray the chicken pieces generously with olive oil spray. Preheat the air fryer to 188°C (370°F). Lightly grease the air fryer basket with a little oil spray.
7Place the chicken in the basket in a single layer without overlapping. Cook for 10–12 minutes, turning the fillets halfway through and spraying again with oil when turning.
8Serve on lightly toasted buns with pickles, lettuce, and mayonnaise (or barbecue sauce).
9For the deep-fried version: heat peanut oil to 200°C (390–400°F). Shake off excess flour and fry for 4–6 minutes until the internal temperature of the chicken reaches 74°C (165°F).