01 - Whisk buttermilk with hot sauce in a large bowl. Add mushrooms and toss to coat thoroughly. Let marinate for 15 minutes to allow flavors to penetrate.
02 - Combine flour, cornstarch, garlic powder, onion powder, smoked paprika, cayenne, salt, and black pepper in a shallow dish. Mix well to distribute spices evenly.
03 - Remove mushrooms from buttermilk, allowing excess to drip off. Press mushrooms into flour mixture, coating completely. For extra crunch, return to buttermilk and dredge a second time.
04 - Heat oil to 350°F in a deep skillet or pot. Fry mushrooms in batches for 4 to 5 minutes, turning occasionally, until golden brown and crispy. Drain on paper towels to remove excess oil.
05 - Melt butter over medium heat in a saucepan. Whisk in flour and cook 1 to 2 minutes until lightly golden. Gradually whisk in milk, then add pepper, salt, and garlic powder. Cook 3 to 5 minutes, whisking constantly, until thickened.
06 - Arrange fried mushrooms on a serving platter. Pour warm gravy over top or serve alongside for dipping. Best enjoyed immediately while crispy.