Put the chicken pieces into a large bowl and sprinkle evenly with kosher salt, garlic powder, and onion powder, tossing to coat well.
Pour in the buttermilk and hot sauce, then mix thoroughly. Cover and chill in the fridge for at least 2 hours, ideally overnight.
In another bowl, combine the flour, cornstarch, kosher salt, paprika, and black pepper and whisk together.
Heat peanut oil in a deep fryer or heavy skillet to 325°F, adjusting temperature down to 300°F if the chicken browns too quickly.
Remove each chicken piece from the marinade letting excess drip off, then dredge thoroughly in the flour mixture. Shake off extra coating and let rest briefly until the breading firms up.
Fry chicken in batches, adding no more than three or four pieces at a time, turning occasionally until golden and cooked through (internal temperature 165°F). Dark meat takes about 12-14 minutes, white meat 8-10 minutes.
Transfer fried chicken to a paper towel-lined tray and immediately sprinkle with flaked salt if desired.
Repeat with remaining pieces until all are cooked and crispy.
