For the brine: Mix the buttermilk, salt and spices together in a medium bowl. Add the chicken, then turn to coat, cover, and refrigerate for at least 4 hours or up to overnight.
For the breading: Mix the flour, salt, baking powder and spices together in a shallow dish or pie plate.
Remove the chicken from the buttermilk brine and transfer to the seasoned flour. Coat the chicken in the seasoned flour, then shake off the excess and return it to the brine. Coat the chicken again in the seasoned flour mixture and transfer to a plate.
Heat the oil in a pan to 375 degrees F.
Fry the chicken, flipping halfway through, until golden brown and the internal temperature reaches 160 degrees F , 6 to 8 minutes. Transfer to a wire rack to drain.
For the honey mustard sauce: Whisk the mustard, honey and mayonnaise together in a small bowl.
For the sandwiches: Apply mayo to the tops of the buns and honey mustard to the bottoms. Place the fried chicken on the bottom buns, then spoon a little honey mustard on top. Lay a slice of Cheddar on each piece of chicken, then the iceberg and sweet onion. Place the top buns on the sandwiches, cut in half, and serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.