Giant Meatballs and Marinara

Name: Giant Meatballs and Marinara
Ingredients: Extra-virgin olive oil, for the baking sheet; 1/4 cup chopped fresh Italian parsley; 3 cloves garlic, smashed and peeled; 1 medium carrot, cut into chunks; 1 stalk celery, cut into chunks; 1 small onion, cut into chunks; 2 large eggs, beaten; 1/4 cup milk; Kosher salt and freshly ground black pepper; 1/2 cup fine dried breadcrumbs; 1/2 cup grated Parmesan; 1 pound ground beef; 1 pound ground pork; 1/4 cup extra-virgin olive oil; 1 medium onion, chopped; 4 cloves garlic, sliced; 1/4 teaspoon crushed red pepper flakes; 1/2 teaspoon dried oregano; Two 28-ounce cans whole San Marzano tomatoes, crushed by hand; Kosher salt; 1 cup grated Parmesan, plus more for serving; 1/2 cup loosely packed fresh basil leaves, chopped