In a bowl, combine buttermilk, salt, and cayenne pepper. Add the chicken and let it marinate in the fridge for at least one hour, or overnight if you have time.

To prepare the ranch slaw, whisk together mayonnaise, sour cream, lemon juice, apple cider vinegar, parsley, dill, salt, and pepper in a large bowl. Mix in the shredded cabbages and julienned carrots, then refrigerate.

Set up a dredging station by combining flour, cornstarch, garlic powder, onion powder, paprika, salt, pepper, and cayenne in a bowl. Dredge the marinated chicken to coat evenly.

Heat oil in a skillet to 350°F. Fry the chicken pieces until they are golden brown and reach an internal temperature of 165°F. Once done, place them on a wire rack to cool slightly.

Toss the crispy chicken in buffalo sauce until coated, or brush it on for a lighter touch.

Toast the brioche buns lightly. Assemble the sandwich by placing the buffalo chicken on the bottom bun and topping it with a generous amount of ranch slaw. Serve immediately for the best flavor.