Use a meat mallet to pound the chicken breasts between two sheets of parchment paper or plastic wrap until they are ½ inch thick. Slice the chicken breasts in half to make two smaller pieces.
In a bowl stir together the buttermilk, hot sauce, and pickle juice. Place the chicken into the buttermilk mixture and leave to soak while preparing the next steps.
Whisk together the flour, salt, pepper, paprika, and onion powder in a shallow bowl.
Heat oil (at least 4” deep, preferably 6” or more) in a Dutch oven. Heat the oil to 350°F. The oil takes 15 minutes or so to heat to temperature. Use a candy or food thermometer to check the temperature. It must be the correct temperature before frying the chicken.
Remove the chicken pieces from the buttermilk mixture, dip into the flour mixture, coating both sides. Then dunk each side once more into the buttermilk and back into the flour mixture -- two full coats of buttermilk then flour.
Carefully drop one chicken piece at a time into heated oil and fry on both sides until cooked through (the center should reach 165°F). The outside should be deep golden brown and crispy. Maintain an oil temperature of 350°F for best results. The chicken cooks up in about 5 minutes.
Place cooked chicken on paper towels or brown paper bags to soak up excess oil.
Meanwhile, prepare buns. Open up each bun and lay it face up on a cookie sheet. Spread a bit of butter over each bun. Broil for 2 to 3 minutes or until buns just begins getting toasty.
To serve, place several pickles on the bottom half of a bun. Top with a piece of fried chicken, Chick-fil-A sauce, and the top bun.
Brioche buns are soft and rich to complement the fried chicken, but you can also use hamburger buns or other sandwich buns.
The longer you let the chicken marinate in the buttermilk, the juicier your chicken will be.
For perfectly fried chicken pieces, be sure they are not too thick (pound to ½-inch). Maintain a decent depth of oil and the proper oil temperature for best results.
For a lighter coating, you can just dip the chicken straight from the buttermilk mixture into the flour mixture, but you don’t get anywhere near the same thick, crispy coating that you will if you do a second round of buttermilk and flour.