Place chicken cutlets in a shallow dish. Mix buttermilk, salt, and pepper. Pour over chicken and let it marinate for at least 30 minutes, or up to 4 hours in the refrigerator.
Prepare the dry dredge mixture: Combine flour, cornstarch, paprika, and garlic powder in a separate shallow dish.
Remove one chicken piece from the buttermilk, letting excess drip off. Dredge thoroughly in the flour mixture, pressing firmly to coat.
Dip the floured chicken back into the buttermilk mixture briefly (just a quick dip).
Return the chicken to the flour mixture and dredge again, ensuring a thick, craggy coating. Set aside on a wire rack. Repeat for all cutlets.
Prepare the spicy mayo: Whisk together mayonnaise, sriracha, smoked paprika, garlic powder, and white vinegar until smooth.
Heat about 2 inches of vegetable oil in a deep skillet to 350 degrees Fahrenheit (175 degrees Celsius).
Carefully place chicken cutlets into the hot oil, ensuring not to overcrowd the pan. Fry for 5 to 7 minutes per side until golden brown and the internal temperature reaches 165 degrees Fahrenheit (74 degrees Celsius).
Remove chicken and place on a clean wire rack set over a baking sheet to drain excess oil. Let the chicken rest for 5 minutes.
Lightly butter the cut sides of the brioche buns and toast them in a dry skillet over medium heat until golden brown.
Assemble the sandwich: Spread a generous amount of spicy mayo on both the top and bottom buns. Place lettuce on the bottom bun, top with the crispy chicken, add pickle chips, and then place the top bun on. Serve immediately.
Notes
For extra crispiness, you can air fry the coated chicken at 380 degrees Fahrenheit (195 degrees Celsius) for 15 to 18 minutes, flipping halfway through.
Use a meat thermometer to confirm the chicken reaches 165 degrees Fahrenheit internally for food safety.
Brioche buns provide a soft contrast to the crunchy chicken; avoid soft white bread that may become soggy quickly.