Prep the Mushrooms: Clean the mushrooms thoroughly, removing any dirt. Trim the stems if necessary, leaving the caps intact.
Make the Batter: In a shallow bowl, combine the cornmeal, flour, garlic powder, onion powder, paprika, salt, pepper, and cayenne (optional).
Dip the Mushrooms: In a separate bowl, whisk together the egg and buttermilk. Dip each mushroom cap into the wet mixture, then dredge it in the seasoned cornmeal mix.
Fry the Mushrooms: Heat about 1-2 inches of vegetable oil in a large skillet over medium-high heat (about 350°F). Fry the mushrooms in batches for 2-3 minutes, until golden and crispy.
Drain and Serve: Use a slotted spoon to remove the mushrooms from the oil. Let them drain on paper towels. Serve hot with dipping sauce of choice.