As I said, I've seen this recipe many times from many different sites on Pinterest, here is one found on the Picky Palate that I happened to pin myself.
I think everyone has their own homemade meatball recipe, I don't usually put mustard in mine, but might try that next time! I also use regular bread crumbs and no milk, but to each his own in this case I think. I also have not seen those cute little balls of mozzarella, so I just cut small squares from a brick.
Delicious! Everyone was pleased, and I was pleased it worked! Perfect for a sandwich, a side dish, an appetizer or on top of spaghetti, this is just so good!!