In a bowl, add buttermilk, egg, kosher salt, garlic powder and cayenne powder. Whisk until combined.
Add chicken thigh fillet. Cover with cling wrap and marinate for 4 hours.
Preparing the breading:
Combine breading ingredients in a bowl and whisk until evenly mixed.
Preparing the dressing:
Mix all dressing ingredients in a smal bowl until fully combined.
Frying the chicken:
Prepare and heat a frying pan or a pot. Add enough oil for frying.
Fry the chicken in batches until browned and crispy. Let it rest for awhile and fry again in a higher heat for a few seconds.
Toasting the buns:
Prepare a skillet and set heat to medium low. Add butter and wait for it to melt.
Cut the buns into halves and toast by place the cut sides into the skillet surface.
Once the buns are nicely toasted, remove from the skillet.
Assembling the sandwich:
Use a spoon to spread both toasted sides of the buns with the dressing. Add a few pieces of pickles, then place a piece of the fried chicken fillet. Finish assembling the sandwich by placing the other half of the toasted bun on top. Enjoy the sandwich.