Step 1

Preheat oven to 450 degrees. Lightly brush a rimmed baking sheet with oil; set aside.

Step 2

Place bread in a bowl and add milk to moisten. Chop bread into small pieces no larger than 1/4-inch and place in a large bowl. Add veal, beef, pork, egg, onion, parsley, oregano, cheeses, salt, and pepper. Using your hands, gently mix until well combined.

Step 3

Divide the mixture into 8 equal portions and roll each portion into a large meatball. Transfer meatballs to prepared baking sheet. Bake until golden brown, 15 to 20 minutes.

Step 4

Meanwhile, bring the marinara sauce to a simmer in a large saucepan. Transfer the meatballs to the marinara sauce and simmer, partially covered, until cooked through, about 30 minutes. Serve immediately with additional Parmigiano-Reggiano.