In a large bowl combine all of the meatball ingredients until well combined. Roll the meat mixture into medium-sized meatballs using your hands.

Melt butter in a deep skillet over medium heat. Brown the meatballs in batches, adding more butter as needed until browned on all sides.

Meanwhile, prepare the gravy by whisking together beef broth, water, flour, ketchup, Dijon mustard, garlic powder, and Worcestershire sauce in a bowl.

Pour the sauce over the meatballs in the pan. Bring to a boil. Reduce heat and simmer for 20-30 minutes, covered, until the meatballs are fully cooked (the internal temperature has reached 160 degrees F.). Served over mashed potatoes.