Preheat the oven to 220°C/gas mark 7. Grease a large baking sheet with oil and set aside. Place the pork, beef, breadcrumbs, garlic, parsley, Grana Padano and eggs in a large bowl. Season with salt and pepper. Mix with your hands until everything is thoroughly combined.
Using dampened hands, take small amounts of the meat mixture and roll into 12 equal-sized balls. Place the balls on the baking sheet. Bake for 12 minutes.
Meanwhile, make the sauce. Put the tomatoes, passata and oil in a large saucepan over a medium heat. Stir in the chilli flakes, basil and some salt. Bring to the boil. Reduce the heat, partially cover the pan and simmer for 10 minutes, stirring occasionally.
Carefully place the meatballs in the tomato sauce and partially cover the pan again. Simmer for 30 minutes, turning the meatballs occasionally. If the sauce gets too thick, add a little hot water. To serve, scatter over a few basil leaves.