Cut each of the 6 chicken breasts in half diagonal ways to create a more uniform thickness (as much as possible) and place in a zip locking bag.
Using a meat tenderizer, or just a heavy rolling pin, pound the chicken breasts until uniform thickness of about ¾ of an inch. Salt and pepper both sides of each piece of chicken.
Pour the 2 cups of buttermilk into the bag and close the zipper. Let the chicken soak in the buttermilk for 30-60 minutes. (Don't go past 30 minutes, if you are using a homemade buttermilk made with lemon/vinegar mixed with regular milk; the acid can begin to toughen and "cook" the chicken. Store bought buttermilk should be ok for longer periods of time.)
Pour oil one half inch deep in a large cast iron skillet and heat oil on medium high heat. (About 350 degrees.)
In a shallow dish, combine the 2 cups flour, 1 ½ teaspoon salt, 1 teaspoon each of onion powder, garlic powder, and paprika, and the 2 teaspoon sugar until evenly mixed.
Once chicken has soaked in the buttermilk mixture, one by one dredge in the flour mixture until evenly coated, and set on a plate. (Discard extra buttermilk left in bag.)
With the hot oil fully heated (it should sizzle when you drop a pinch of flour in), lay the chicken pieces in the oil leaving at least an inch of space between each piece; you may need to work in batches if they don't all fit. Fry on one side for 4-6 minutes and flip over to fry on the other side until both sides are golden brown and chicken is cooked through. Transfer finished chicken pieces to wire rack to drain, over a plate or parchment line baking sheet. (Do not lay them directly on paper towels or on plate, see notes.)