Step 1: In a large mixing bowl, gently combine the ground beef and ground pork. Be careful not to overmix at this stage.
Step 2: Add the fresh breadcrumbs, Parmesan cheese, Pecorino Romano cheese, fresh parsley, fresh basil, minced garlic, beaten eggs, milk, salt, and black pepper to the meat mixture.
Step 3: Using clean hands, gently mix all ingredients until just combined. Ensure no dry pockets remain, but avoid overworking the meat, which can lead to tough meatballs.
Step 4: Using a 1.5-inch cookie scoop or a tablespoon, form the mixture into approximately 24 uniform meatballs. Roll gently between your palms to smooth them out.
Step 5: Place the formed meatballs on a parchment-lined baking sheet and refrigerate for at least 30 minutes to help them firm up.
Step 6: Choose your cooking method: For pan-frying, heat 2 tablespoons of olive oil in a large, heavy-bottomed skillet over medium-high heat. Brown the meatballs in batches on all sides, about 5-7 minutes per batch. For baking, preheat oven to 400°F (200°C). Arrange meatballs on a parchment-lined baking sheet and bake for 20-25 minutes, or until cooked through and lightly browned.
Step 7: Transfer the cooked (browned or baked) meatballs into your simmering marinara or tomato sauce. Let them gently simmer in the sauce for at least 30-60 minutes to absorb flavors and become incredibly tender. Serve hot with your favorite pasta or in a sub.