Meatballs stuffed with mozzarella and pesto

First make the pesto: lightly toast the pine nuts in a dry pan. Grind the toasted pine nuts, Parmesan and garlic in the food processor until the mixture forms small crumbs. Add the basil, salt, pepper and olive oil and mix again briefly.Use your hands to mix the ground beef with the egg, breadcrumbs, salt, pepper and thyme. Spoon a little pesto on top of each mozzarella ball and then cover the whole ball with the minced beef mixture.Heat a tablespoon of oil in a large frying pan and fry the meatballs until golden brown. Add the passata (tomato sauce) and stir carefully. Leave to simmer gently for another few minutes. Serve with grated Parmesan and a few basil leaves.