In a large bowl, whisk together the buttermilk, garlic powder, onion powder, paprika, black pepper, and salt. Add the chicken thighs and ensure they’re fully submerged. Cover and refrigerate for at least 4 hours or overnight for best results.
Heat oil in a Dutch oven to 350°F.
Mix flour, cornstarch, paprika, oregano, thyme, and chili powder in a shallow dish.
Remove the chicken from the marinade, allowing excess to drip off, then dredge in the flour mixture, pressing to adhere.
Fry chicken in batches until golden brown and cooked through, about 6–8 minutes per piece depending on thickness. Drain on a wire rack.
Leave chicken in a warm oven while you make waffles.