How to Make It
In a large bowl, toss the chicken with the buttermilk. Cover with plastic wrap and refrigerate the chicken for at least 8 hours or overnight.
In a large, resealable plastic bag, combine the flour, salt, pepper and cayenne. Set 2 large racks over rimmed baking sheets. Working in batches, drain the chicken, scraping off most of the buttermilk against the side of the bowl. Add the chicken to the bag, a few pieces at a time, and shake to coat completely. Transfer the chicken to the racks, pressing the flour to help it adhere as you remove the chicken from the bag.
Pour 1 inch of oil into each of 2 large cast-iron skillets and heat to 350 degrees. Add about half of the chicken pieces to the hot oil, being sure not to crowd the skillet. Fry over moderate heat until the chicken is golden, crisp and cooked through, 20 to 25 minutes; an instant-read thermometer should register 165 degrees for thighs or drumsticks and 160 degrees for breasts. Line the racks with paper towels and drain the chicken. Continue frying the chicken in batches, being sure the oil temperature stays at 325 degrees during frying. Serve warm or at room temperature.