1/2 pound ground beef
1/2 pound ground pork
1/2 pound ground veal
1/2 cup panko (Japanese breadcrumbs)*
1/2 cup water
8 tablespoons freshly grated Pecorino Romano cheese, divided
1 large egg
1 large egg yolk
1/4 cup plus 2 tablespoons chopped fresh parsley
1 teaspoon salt
1/2 teaspoon ground black pepper
1/4 cup vegetable oil
2 tablespoons olive oil
1 cup chopped onion
6 garlic cloves, chopped
1/4 cup (packed) fresh basil leaves
1 1/2 teaspoons fennel seeds
1 28-ounce can whole peeled tomatoes
1 14.5-ounce can whole peeled tomatoes
Arugula leaves (optional)
18 small soft rolls, split horizontally
*Sold in the Asian foods section of some supermarkets and at Asian markets.