In a medium bowl, combine egg, breadcrumbs, milk, and seasonings. Add in beef and parmesan cheese (if using) and combine until just mixed through, being careful not to overmix.
Using a 2 Tablespoon cookie scoop (or a spoon), make 12-16 meatballs. Wet hands and gently roll mixture in your palms to create round balls. Lay the meatballs in a single layer, about ½ inch apart in the air fryer basket.
Bake the meatballs for 13-18 minutes or until meatballs reach an internal temperature of 160°F.
Nutrition calculated without optional parmesan cheese.
Remember to only mix ingredients with the beef until just combined.
Rest meatballs for 5 minutes before serving.
Refrigerate cooked and cooled meatballs in a covered container for 4-5 days. Freeze individually on a baking sheet, then transfer to a zippered bag, and freeze for up to 4 months.