Mix the buttermilk and 2 tablespoons of Frank's RedHot together in a large bowl. Add the chicken pieces and toss them to coat with the sauce.
Combine the flour, black pepper, garlic powder, paprika, cayenne pepper, and salt together in a large, shallow dish.
Working with just a few pieces at a time, transfer the chicken to the flour mixture, allowing excess buttermilk to drip off first. Coat the chicken pieces in the flour mixture and transfer them to a wire rack. Repeat these steps so that each piece of chicken is double coated. Place the coated chicken in the refrigerator for at least 30 minutes.
Heat 3 inches of canola oil over medium-high heat in a large, heavy pot until the temperature reaches 375 F. Prepare a wire rack over a rimmed baking sheet lined with aluminum foil.
Working in batches, fry the chicken until golden brown, turning occasionally, for about 5-10 minutes. Transfer the chicken to the prepared wire rack.
Melt the butter in a medium saucepan over medium heat. Add the remaining ¾ cups of Frank's RedHot and stir until it is combined with the butter and heated through.
Add the cooked chicken pieces to a large bowl. Pour the prepared buffalo sauce over the chicken and stir until each piece is completely coated.
Serve immediately with celery sticks and ranch dressing.