Add the finely diced onion to the bubbling butter and sauté for about 5 minutes, until soft.
Add the sliced mushrooms and cook for a few minutes until they start to brown around the edges.
Add the baby spinach and sauté until wilted, then season with salt and pepper.
Stir in the sour cream and cook for 1 minute.
Add the shredded cooked chicken and stir to combine.
Stir in the grated Parmesan and cook for about 30 seconds. Taste and adjust seasoning, then remove from the heat and let the filling cool slightly.
Whisk the egg until loose and brush about 1.5cm of egg wash around the edge of each tortilla.
Divide the filling into 4 portions and spread each onto the centre of a tortilla. Fold each tortilla over and press the edges to seal.
Brush the tops of each sealed pie with egg wash.
Preheat the air fryer (Instant Vortex Versazone) to 180C for 19 minutes. Once heated, place the pies in the basket and air-fry for 12 minutes, until golden brown.
Open the air fryer, flip the pies, brush the other side with egg wash, and air-fry for a further 7 minutes until golden brown.