Mix together the butter, chopped parsley and crushed garlic. You can use a food processor to do this, just don't over process it or the butter will go too soft.
Divide the butter out into 12 (ish) equal sized balls. Pop them in the fridge (or freezer if you are short on time), to harden up.
If you are using whole chicken breasts instead of already minced/ground meat then you will need to also run this through a food processor, or high speed blender.
Once your garlic butter balls have hardened up a little, it's time to start wrapping your ground chicken around them. Take a little bit of chicken at a time and wrap some around each butter ball as a thin layer, around 1 to 1.5cm.
Beat the egg in a bowl, ready to dip your chicken balls in. Set up another bowl with your breadcrumbs in. You can use day old bread and pop it in a food processor to turn it into small crumbs, or as I often like to do, keep some store bought breadcrumbs in the cupboard. Season your breadcrumbs depending on your tastes (salt, pepper, perhaps a little paprika if you want some extra flavour).
For the next step (and final part of the preparation!) I use some kitchen tongs. It makes it easier to dip the balls and ensure they are evenly coated all over. Firstly dip the ball in the egg bowl, then roll it around in the bowl of breadcrumbs. Make sure the breadcrumbs are holding on tight or the air fryer might blow them off. If need be use your hand to press them in firmer.
I sprayed them with a little oil (using an oil sprayer) and then placed them in my air fryer basket. I cooked them for 10 minutes at 200C/390F). Check half way through and turn over.
Notes
Side note: some people like to include some flour to this part of the process - they feel it helps the breadcrumbs hold to the meat better. I personally prefer to omit it (I don't notice a difference). If you want to include flour just dip the balls in the flour before the egg.