01 - Whisk buttermilk with hot sauce in a large bowl. Add mushrooms and toss to coat completely. Allow to marinate for 15 minutes to tenderize and absorb flavor.
02 - Combine flour, cornstarch, garlic powder, onion powder, smoked paprika, cayenne pepper, salt, and black pepper in a shallow dish. Mix thoroughly to distribute spices evenly.
03 - Remove mushrooms from buttermilk, allowing excess to drip off. Press firmly into flour mixture to coat thoroughly. For extra-crispy results, return mushrooms briefly to buttermilk and repeat dredging process.
04 - Heat vegetable oil in deep skillet or pot to 350°F. Fry mushrooms in small batches for 4-5 minutes, turning occasionally, until golden brown and crispy. Transfer to paper towel-lined plate to drain excess oil.
05 - Melt butter over medium heat in saucepan. Whisk in flour and cook 1-2 minutes until lightly golden. Gradually whisk in milk, then add pepper, salt, and garlic powder. Continue whisking constantly for 3-5 minutes until thickened and smooth.
06 - Arrange crispy fried mushrooms on serving platter. Pour warm gravy generously over top, or serve alongside for dipping. Enjoy immediately while hot and crisp.