Combine mince, breadcrumbs, parmesan, egg, herbs and half the garlic in a large bowl. Season with salt and pepper. Mix well. Roll level tablespoons of mixture into balls. Sprinkle with flour. Toss to coat.
Cook pasta in a large stockpot of boiling, salted water until tender. Drain. Cover to keep warm.
Heat half the oil in same large stockpot over a medium to high heat. Add meatballs in two batches. Cook, turning occasionally, for about 4 minutes, or until browned and almost cooked. Remove. Cover to keep warm.
Heat remaining oil in same pot over a low heat. Add onion. Cook, stirring, until soft. Add passata and stock. Season with salt and pepper. Bring to boil. Simmer, covered, stirring occasionally, for 10 minutes.
Return meatballs to pot. Simmer, uncovered, for a further 5 minutes, or until cooked through. Stir in spaghetti and basil. Garnish with basil .