Place chicken breasts between parchment paper and pound to a uniform 1.5cm thickness using a meat mallet.

In a large bowl, whisk together buttermilk, 5g salt, 2g pepper, and smoked paprika.

Submerge chicken in the buttermilk marinade and refrigerate for 30 minutes.

In a shallow tray, combine flour, cornstarch, garlic powder, onion powder, cayenne pepper, and remaining salt and pepper.

Heat vegetable oil in a heavy-bottomed Dutch oven to 175°C (350°F).

Remove chicken from marinade, letting excess drip off, then dredge in the flour mixture, pressing firmly to create crags in the coating.

Carefully lower chicken into the oil and fry for 3-4 minutes per side until the internal temperature reaches 74°C (165°F) and the exterior is golden brown.

Transfer chicken to a wire rack to drain for 3 minutes to maintain crust integrity.

Toast brioche buns in a dry pan over medium heat until golden.

Assemble by spreading mayonnaise on the bottom bun, followed by lettuce, tomato, the crispy chicken, and the top bun.