Pour buttermilk into a shallow baking dish and add the chicken breasts, turning to coat fully. Let soak for 30 minutes.
In a separate shallow dish, whisk together flour, cornstarch, paprika, garlic powder, onion powder, and salt.
Drizzle a couple spoonfuls of the buttermilk from the chicken dish into the flour mixture and stir gently to create small clumps.
Lightly season each chicken breast with salt.
Dredge each piece in the flour mixture, pressing to coat both sides evenly.
Shake off excess flour and place coated chicken on a cooling rack set over a baking sheet.
While chicken rests, heat 3 inches of oil in a large skillet to 350°F.
Carefully lower each chicken breast into the hot oil and fry for 5–6 minutes on one side.
Flip gently and fry for an additional 4–5 minutes, or until golden brown, crispy, and cooked through.
Transfer the fried chicken to a clean cooling rack and sprinkle lightly with salt.
In a small bowl, mix together mayonnaise and hot sauce until smooth.
Spread spicy mayo on both top and bottom halves of the buns.
Layer pickle slices on the bottom bun, then top with a piece of fried chicken.
Add the top bun, press gently, and serve immediately.