Preheat the air fryer to 400F. Line an air fryer tray with parchment paper.
Combine the buttermilk ingredients in a bowl. Whisk, and set aside for 5 minutes.
Combine all dry batter ingredients in a separate bowl.
Set up a batter station, with the mushrooms in a bowl, then the dry batter, wet batter, and baking sheet. One at a time using tongs, dip the mushrooms in the flour mix, then the buttermilk. Repeat again, and then place the battered mushrooms onto the baking sheet.
Spray with a little bit of oil. Place in the air fryer for six minutes, then flip and cook for an additional 6 minutes until crispy.