Preheat the air fryer: Set to 380°F (193°C) for about 4 minutes. A warm basket helps the meatballs brown quickly.
Mix the binder: In a large bowl, whisk the egg, milk, Worcestershire, salt, and pepper.
Stir in breadcrumbs and let sit 2 minutes to hydrate.
Add flavor: Fold in Parmesan, garlic, onion, and parsley. This spreads the aromatics evenly so every bite tastes great.
Add the beef: Gently mix in the ground beef with your hands or a fork until just combined. Do not overmix or the meatballs will turn dense.
Shape: Scoop about 1 1/2 tablespoons per meatball (golf-ball size). Lightly roll to smooth.
You should get 16–18 meatballs.
Prep the basket: Lightly spray the air fryer basket with olive oil spray to prevent sticking.
Arrange: Place meatballs in a single layer with a little space between them. Work in batches if needed; crowded baskets steam instead of brown.
Air fry: Cook at 380°F (193°C) for 9–12 minutes, shaking the basket or turning once around the 6-minute mark if you want deeper color. Cook to 160°F (71°C) internal temperature.
Rest and serve: Let the meatballs rest 3 minutes to reabsorb juices. Toss with warm marinara, serve over pasta, stuff into rolls with mozzarella, or set out with toothpicks and dipping sauces.