In a large bowl, combine broccoli, onion, mushrooms, egg, sour cream, mayonnaise, salt and pepper.
Spoon mixture into a round cake barrel.
Preheat air fryer at 180°C for 3 minutes.
Cook casserole for 14 minutes.
Remove barrel from air fryer and let rest for 10 minutes.
Evenly distribute crushed Cheddar cheese crisps over the top of casserole and serve warm.