In a large mixing bowl, combine the ground beef, egg, parmesan, and onion powder. Mix together by hand.

Use a tablespoon to measure out and shape the meatballs.

Preheat a saucepan over medium heat. Add the meatballs and cook until browned on the outside (if they're still slightly pink in the middle, that's okay for now). Set aside.

In the same saucepan, add the water, apple cider vinegar, soy sauce, sugar-free ketchup, and erythritol. Whisk until the sauce comes together. Slowly whisk in the xanthan gum. Add only a little at a time, waiting a couple minutes in between to make sure it thickens first. Lower the temperature and let the sauce simmer on low.

After a couple of minutes, check the sauce for the desired consistency. Run a spoon through the sauce to see whether it coats the back — a properly thickened sauce will not immediately run back together. Add the meatballs and let simmer on low for 10 minutes or until the meatballs are cooked through.

Serve and enjoy!