01 - Whisk buttermilk with hot sauce in a large bowl. Add mushrooms and toss to coat thoroughly. Let marinate for 15 minutes to absorb flavors.
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 each mushroom into the flour mixture to coat thoroughly. For extra crunch, dip back into buttermilk and dredge again in flour.
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. Transfer to a paper towel-lined plate to drain.
05 - Melt butter over medium heat in a saucepan. Whisk in flour and cook for 1 to 2 minutes until lightly golden. Gradually whisk in milk, then add pepper, salt, and garlic powder. Cook, whisking constantly, until thickened, about 3 to 5 minutes.
06 - Arrange fried mushrooms on a serving platter. Pour warm gravy over the top or serve alongside for dipping. Best enjoyed immediately while crispy.