Cut chicken into uniform 1.5-inch pieces and pat dry with paper towels.
Combine chicken with buttermilk, hot sauce, and half the spices (cayenne, garlic powder, onion powder, smoked paprika, pepper, salt). Cover and refrigerate for at least 30 minutes.
In a separate bowl, whisk together flour, cornstarch, baking powder, and the remaining spices.
Remove chicken from marinade, let excess drip off, then coat in flour mixture. Dip back in buttermilk, then coat again in flour mixture, pressing firmly to adhere.
Place coated nuggets on a wire rack and let rest for 10 minutes. This helps the coating adhere during frying.
Heat oil in a Dutch oven to 350°F (175°C). Preheat oven to 200°F (95°C) to keep cooked batches warm.
Working in batches of 6-8 nuggets, fry for 4-5 minutes, turning once or twice, until deep golden brown and internal temperature reaches 165°F (74°C).
Transfer to a wire rack to drain. Sprinkle with salt and extra cayenne if desired. Serve hot with your choice of dipping sauces.