01 - Combine buttermilk and hot sauce in a large bowl. Add chicken pieces, turn to coat thoroughly. Cover and refrigerate for at least 1 hour, up to overnight for maximum tenderness.
02 - Preheat oven to 450°F. Whisk together flour, baking powder, baking soda, salt, and sugar. Cut cold butter into mixture until it resembles coarse crumbs. Stir in buttermilk just until dough forms.
03 - Turn dough onto floured surface, pat to 1-inch thickness. Cut with 2.5-inch round cutter. Place on parchment-lined baking sheet. Bake 12–15 minutes until golden brown. Cool slightly.
04 - Mix flour, salt, pepper, paprika, garlic powder, onion powder, and cayenne in shallow dish. Remove chicken from marinade, let excess drip off. Press chicken into flour mixture to coat thoroughly.
05 - Heat 1 inch oil to 350°F in deep skillet or Dutch oven. Fry chicken in batches, turning occasionally, until golden brown and internal temperature reaches 165°F, about 12–15 minutes. Drain on wire rack.
06 - Melt butter over medium heat. Whisk in flour, cook 1–2 minutes. Gradually whisk in milk until smooth. Cook, stirring constantly, until thickened, 4–5 minutes. Season with salt, pepper, and garlic powder.
07 - Place warm biscuits on plates. Top with fried chicken pieces. Spoon gravy generously over biscuits and chicken. Serve immediately while hot.