Brining the chicken in buttermilk and seasoning overnight is the key to this moist, succulent dish.
Put buttermilk, 1/4 cup salt, and the hot sauce (if desired) in a large, airtight container. Add chicken pieces; turn to coat. Cover; refrigerate 2 hours or overnight.
Preheat oven to 200 degrees. Put flour, remaining 5 teaspoons salt, pepper, cayenne, and baking powder in a large resealable plastic bag. Shake vigorously.
One at a time, place chicken pieces in bag, and shake to coat. Remove from bag, and shake off any excess. Transfer coated pieces to a wire rack set over a baking sheet. Let stand 30 minutes.
Heat shortening (and bacon drippings, if desired) in two 10-inch cast-iron skillets over medium-low heat until it registers 375 degrees on a deep-fry thermometer. (Alternatively, use one skillet and half the shortening and drippings, and cook in batches.) Using tongs, place thighs and drumsticks in skillets. Fry until undersides are dark golden, 10 to 14 minutes. Turn pieces over; cook until dark golden all over and an instantread thermometer inserted into the thigh registers 170 degrees, another 10 to 14 minutes.
Transfer to a wire rack (clean the rack that held raw pieces before reusing it) set over a baking sheet. Transfer rack and sheet to oven to keep chicken warm.
Remove any bits of coating left in skillets with a slotted spoon; discard. Repeat process to fry breasts and wings, 10 to 14 minutes per side (cook until an instantread thermometer inserted into the breast registers 170 degrees).
Because dark meat can take longer to cook, fry it separately from white meat. Small chickens called fryers are tender and best for frying. Use coarse salt in this recipe; table salt will be too salty.