Place chicken thighs in a gallon sealable bag.
Whisk together buttermilk, sour cream, hot sauce, ½ teaspoon garlic powder,1 teaspoon salt, and 1 teaspoon pepper in a medium bowl. Pour buttermilk mixture into the bag.
Seal and turn to evenly coat. Allow chicken to rest in the fridge for 2 hours (up to 8 hours in fine).
Preheat oven to 425°F. Line a rimmed baking sheet with foil, add a wire rack and lightly spray rack with cooking spray. Add flour, paprika, thyme, cornstarch, ½ tsp, 1 teaspoon salt, 1 teaspoon pepper in a large resealable bag. Take the chicken out of the marinade bag, shake off excess marinade, and add a piece chicken to the flour bag.
Shake, the remove, and shake off excess flour coating and place on the rack. Repeat with remaining chicken. Throw out the remaining marinade and flour mixture.
Bake 45-50 minutes until golden brown and the internal temperature reads 165°F in the thickest part of the meat.