For The Meatballs
2 slices white or sandwich bread, torn into 1-inch pieces
1/2 cup whole milk
8 ounces ground beef
8 ounces ground pork
4 ounces ground veal
1/2 cup finely grated pecorino Romano or Parmesan cheese (1 ounce)
3 tablespoons coarsely chopped fresh flat-leaf parsley
1 garlic clove, minced
1 large egg
Coarse salt
Marinara Sauce
For The Sandwiches
2 dozen brioche rolls, split
1 1/2 cups coarsely grated mozzarella cheese (5 ounces)
1/2 cup finely grated pecorino Romano or Parmesan cheese (1 ounce)
Small basil leaves
Make the meatballs: Soak bread in milk for 5 minutes. Gently mix bread and milk with meats, pecorino Romano, parsley, garlic, egg, and 1 teaspoon salt. Refrigerate for at least 30 minutes.
Roll mixture into twenty-four 1-ounce balls (each about the size of a golf ball).
Heat sauce in a large heavy pot over medium heat. Drop meatballs into sauce, and bring to a gentle simmer. Cook, partially covered, until meatballs are cooked through, 20 to 25 minutes.
Make the sandwiches: Preheat oven to 400 degrees. Working in batches, arrange rolls, cut side up, on a baking sheet. Place 1 meatball, a spoonful of sauce, 1 tablespoon mozzarella, and 1 teaspoon pecorino Romano on bottom halves. Bake until cheese melts, about 3 minutes. Sandwich with basil.
Recipe found here.