Pat the chicken pieces dry with kitchen paper.
In a large bowl, whisk together the buttermilk, hot sauce, salt, black pepper, garlic powder, onion powder and paprika.
Add the chicken pieces to the marinade, toss to coat, then cover and chill in the fridge for at least 4 hours or overnight.
Take the chicken out of the fridge 30 minutes before frying to bring it closer to room temperature.
In a shallow dish, whisk together the plain flour, cornflour, baking powder, salt, black pepper, paprika, garlic powder, onion powder and cayenne pepper.
Working one piece at a time, dredge each chicken piece in the flour mixture, pressing the coating on firmly; place the coated pieces on a wire rack set over a baking tray and leave to rest for 10-15 minutes.
Pour the oil into a large, deep, heavy-based saucepan and heat over a medium-high heat until it reaches around 170°C.
Carefully lower 3–4 pieces of chicken into the hot oil and fry for 10-15 minutes, turning occasionally, until golden brown and the thickest part reads 75°C on a probe thermometer.
Transfer the chicken to a wire rack set over kitchen paper to drain off any excess oil.
Repeat with the remaining chicken, ensuring the oil returns to temperature between batches.
Serve immediately. Store any leftovers in an airtight container in the fridge for up to 3–4 days.