Step 1

Using your hands, gently mix together the pork, beef, breadcrumbs, Parmesan cheese, salt, eggs, garlic, and parsley in a large bowl. Form mixture into 2-inch balls.

Step 2

Heat the oil in a large oven-safe skillet over medium-high heat. Add the meatballs; cook, turning, until browned all over, about 10 minutes. Use a slotted spoon to transfer to a plate.

Step 3

Reduce the heat to medium. Add onion and pepper flakes; cook, stirring occasionally, until onion is tender. Add the tomatoes and basil; simmer, stirring frequently, until the sauce is slightly thickened. Return the meatballs and its juices to pan. Simmer, turning meatballs until cooked through.

Step 4

Heat the broiler and arrange the mozzarella cheese on top of the meatballs. Broil until melted, about 2 minutes. Serve immediately.