Combine the veal, pork, beef, bread, milk, egg, Parmesan, pecorino, parsley, salt, pepper and garlic in a stand mixer fitted with the flat blade. Mix on medium-low speed for 1 minute.
Scoop out 2-tablespoon pieces of meat and gently roll them between your hands into balls about the size of a golf ball. The meat will be soft, so don¿t compress it too much. Put the flour in a bowl and toss the meatballs in the flour as you work.
Heat the grapeseed oil over medium heat in a large skillet and, working in batches, add the floured balls, cooking them until golden brown all over, 8 to 10 minutes total. The internal temperature should be about 155 degrees F.
Divide the meatballs among plates; sprinkle with Parmesan and parsley.
Recipe courtesy of Marc Vetri, Adapted from "Rustic Italian Food" (Ten Speed Press, November 2011).