Combine buttermilk, garlic powder, onion powder, salt, and black pepper in a bowl. Add chicken pieces, ensuring they are fully coated, then refrigerate for at least 2 hours or overnight.

In a separate shallow dish, whisk together flour, cornstarch, paprika, cayenne pepper (if using), salt, and black pepper.

Remove chicken from the marinade, allowing excess to drip off, then dredge each piece thoroughly in the flour mixture, pressing to ensure a thick, even coat.

Heat vegetable oil in a large heavy-bottomed pot or Dutch oven to 350°F (175°C). Carefully add chicken pieces, ensuring not to overcrowd the pot, and fry for 6-8 minutes per side or until golden brown and cooked through.

Once cooked, transfer fried chicken to a wire rack set over a baking sheet to drain excess oil. While chicken rests, melt butter in a small saucepan over medium heat, then add minced fresh garlic and sauté for 1 minute until fragrant.

Brush the hot garlic butter generously over the fried chicken pieces. Garnish with fresh chopped parsley and serve immediately.