mix together bread crumbs with milk in a small bowl and set aside
heat some olive oil in a skillet over medium. Add your diced onion. Cook and stir until soft and translucent, about 10 minutes. Set aside and let them cool down.
in a large mixing bowl, add your beef, onions, bread crumb mixture, eggs, italian seasoning, salt, garlic, onion and if using the parsley and parmesan as well.
using about 2 tbsp of meat, form mixture into meatballs and set on a baking sheet. Optional: if you have the time, it would be good to refrigerate them for 30 min- 1 hour.
get your breading station ready. Using 3 shallow plates, add your flour, whisked egg and breadcrumbs. If using the optional parmesan, mix this into your breadcrumbs
Dip your meatballs into the flour until well coated. Then the egg wash and then the breadcrumbs. Set back onto baking sheet.
Preheat your air fryer to 400F for 8-10 minutes
Turn down to 375 F. Spray the cage with olive oil non stick spray
Add your meatballs, being careful to not overcrowd. Spray the top of them with more non stick spray
Cook for 8- 10 minutes or until the center reaches 165F