In a large bowl, combine buttermilk, pickle juice, kosher salt, hot sauce, and black pepper. Add chicken pieces, ensuring they're fully submerged. Cover and refrigerate for at least 2 hours, ideally overnight.

In a large shallow dish, whisk together flour, cornstarch, garlic powder, onion powder, paprika, salt, and black pepper.

Pour oil into a large, heavy-bottomed pot or deep cast-iron skillet to a depth of about 2 inches. Heat to 350°F (175°C).

Remove chicken pieces from the buttermilk brine, letting excess drip off. Thoroughly coat each piece in the flour mixture, pressing gently to adhere. Shake off excess.

Carefully place chicken pieces in hot oil, working in batches to avoid overcrowding. Fry until golden brown and cooked through (165°F/74°C internal temperature), about 12-15 minutes for larger pieces, 8-10 minutes for smaller pieces.

Transfer fried chicken to a wire rack set over a baking sheet. Allow to drain for 5 minutes.

While the chicken rests, reserve 1/2 cup of the frying oil. In a heat-resistant bowl, combine the hot oil ingredients, whisking until smooth.

Using a pastry brush, generously coat each piece of fried chicken with the hot oil mixture. The more you apply, the spicier it will be.

Place hot chicken on slices of white bread, garnish with pickle slices, and serve immediately.