Place the ground beef, onions, and breadcrumbs in a bowl. Pour the milk and eggs directly over the breadcrumbs, allowing them to soak in the moisture. Sprinkle it with salt and pepper. Use your hands to gently combine and bring the mixture together.

Make a foil “sling” to hold and transfer your meatloaf. Layer two pieces of foil that are about double the length of your air fryer.

Place the ground beef mixture into the center of the foil and form a loaf measuring about 6-7 inches long, 4 inches wide, and 2-3 inches high. Fold the edges up on either end of the loaf so you can lift it and place it in the air fryer.

Air fry at 370 degrees F for 15 minutes. Cover the meatloaf with a piece of foil, and continue cooking at 370 degrees F for another 15 minutes.

Meanwhile, in a small bowl, whisk together ketchup, brown sugar, and mustard. When the timer goes off, slather the mixture all over the top of the meatloaf, then continue cooking for another 10-15 minutes, or until internal temperature reaches 160 degrees F.

Allow the meatloaf to rest for 10 minutes before slicing and serving.