Chop the leeks and pepper, peel and chop the carrot.
In a large pan set over a medium heat, add the butter and allow it to melt.
Add the chopped leeks and sautee for 2-3 minutes.
Add the carrot, pepper and garlic, give it a good stir, and sautee for a further 2-3 minutes.
Add the shredded chicken, pour in the chicken stock, place a lid on pan, and leave it to simmer to 10-15 minutes or until the veggies are tender.
If you think the filling hasn't got enough liquid left, you can add a bit more stock.
Add the milk and cornflour slurry (cornflour mixed with 2 tablespoons of water).
Stir well until the mixture thickens into a sauce.
Season with salt, pepper and herbs, and remove the pan from the heat.
Leave the chicken filling to cool down completely.
Use a large cookie cutter to cut out puff pastry rounds that would fit around a foil / aluminum muffin or mini pie case.
Divide the cold filling between 6 foil cases ( or ramekins if you don't have disposable pie cases), and top with the pastry lid.
Seal the lids well by pinching firmly around the edges, and use a sharp knife to make a cut in the middle of the lid, that will allow the steam to escape.
Place the mini pies in the air fryer drawers - I have a Tefal air fryer with 2 drawers, a large one which can fit in 4 mini pies, and a small one which can fit in 2 pies.
Air fry for 12-13 minutes at 180 degrees Celsius (350 Fahrenheit) or until the pastry lids are golden.