In a large mixing bowl, combine ground beef, breadcrumbs, egg, and milk. Stir in chopped onion, parsley, garlic powder, all-spice, salt, and pepper until just combined.

Grab a portion of the mixture and roll it into balls about 1 inch in diameter. Place on a plate.

Preheat air fryer to 375°F (190°C) for about 5 minutes. Arrange meatballs in a single layer in the basket and lightly spray with cooking oil.

Cook meatballs for 12-14 minutes, shaking the basket halfway through, until golden brown and reaching an internal temperature of 160°F (71°C).

In a skillet over medium heat, melt butter and olive oil. Whisk in flour to create a roux, then add beef broth gradually, stirring to avoid lumps. Stir in cream, mustard, Worcestershire sauce, salt, and pepper, cooking until thickened.

Carefully transfer cooked meatballs into the skillet with the sauce and stir gently. Simmer for an additional 2-3 minutes.