01 - Whisk buttermilk with hot sauce in a large bowl. Add mushrooms and toss to coat completely. Let marinate for 15 minutes to tenderize and absorb flavor.
02 - Combine flour, cornstarch, garlic powder, onion powder, smoked paprika, cayenne, salt, and black pepper in a shallow dish. Mix thoroughly to distribute spices evenly.
03 - Remove mushrooms from buttermilk, allowing excess liquid to drip off. Press firmly into flour mixture to coat thoroughly. For extra-crispy results, double-dip: return to buttermilk, then dredge in flour mixture again.
04 - Heat vegetable oil in a deep skillet or pot to 350°F. Fry mushrooms in batches without overcrowding, 4–5 minutes, turning occasionally until golden brown and crispy. Drain on paper towel-lined plate.
05 - Melt butter in saucepan over medium heat. Whisk in flour and cook 1–2 minutes until lightly golden. Slowly whisk in milk to prevent lumps. Add black pepper, salt, and garlic powder. Cook, whisking constantly, until thickened, 3–5 minutes.
06 - Arrange fried mushrooms on serving platter. Pour warm gravy generously over top or serve alongside for dipping. Serve immediately while crispy.