Mix buttermilk, pickle juice, and cayenne in a bowl.
Add chicken tenders and submerge fully in the marinade.
Cover and refrigerate for at least 2 hours or overnight.
Whisk together flour, cornstarch, garlic powder, onion powder, paprika, salt, and black pepper in a shallow dish.
Remove tenders from marinade, letting excess drip off.
Coat each tender thoroughly in the flour mixture.
Place coated tenders on a wire rack and let rest for 20 minutes at room temperature.
Heat 3 inches of peanut oil in a Dutch oven to 350F.
Fry tenders in batches of 4-5 for 6-8 minutes, flipping halfway, until golden brown and internal temperature reaches 165F.
Transfer to a wire rack to drain.
Season immediately with extra salt while hot.