Whisk together buttermilk, eggs, hot sauce, pickle juice, salt, black pepper, and garlic powder in a large mixing bowl until fully combined.
Add chicken pieces to the buttermilk mixture and submerge completely, then cover with plastic wrap and refrigerate for at least 4 hours or overnight.
Combine flour, cornstarch, paprika, garlic powder, onion powder, salt, black pepper, and cayenne pepper in a shallow dish and whisk until evenly mixed.
Remove chicken from refrigerator 30 minutes before frying to bring to room temperature for even cooking.
Lift each chicken piece from buttermilk, let excess drip off, then press firmly into seasoned flour to coat all sides completely.
For extra crispy coating, dip floured chicken back into buttermilk and dredge in flour mixture a second time.
Place coated chicken pieces on a wire rack and rest for 10 minutes to help the coating set and adhere properly.
Pour vegetable or peanut oil into a cast iron skillet or Dutch oven until 2 inches deep and heat to 325°F using a deep-fry thermometer.
Carefully lower chicken pieces into hot oil in batches without overcrowding and maintain oil temperature between 300°F and 325°F throughout cooking.
Fry chicken for 15 to 18 minutes, flipping halfway through, until golden brown and internal temperature reaches 165°F for breasts or 175°F for dark meat.
Transfer fried chicken to a wire rack set over a baking sheet and let drain for 2 to 3 minutes.
Combine cayenne pepper, brown sugar, paprika, garlic powder, and salt in a heat-safe bowl while chicken drains.
Carefully ladle half cup of hot frying oil into the spice mixture and whisk vigorously until a smooth paste forms.
Use a pastry brush to generously coat each piece of fried chicken with the spicy oil paste, covering all sides and crevices.
Place white bread slices on serving plates and top with spicy coated chicken pieces and dill pickle chips, then serve immediately.
