1. Heat the oven to gas 6, 200˚C, fan 180˚C. Heat the oil in a deep frying pan set over a medium-high heat and fry the onion for 7-10 mins until tender. Add the garlic for another min, then stir in the beef mince. Cook, stirring occasionally, for 8-10 mins until golden brown and any liquid has been absorbed.
2. Stir in the tomato purée for 1 min, then tip in the chopped tomatoes and half a can of water. Season and gently simmer for 10 mins until the sauce has thickened slightly.
3. Meanwhile, cook the spaghetti for 6 mins, then drain and tip into a 25 x 15cm baking dish. Spoon over three-quarters of the white sauce, then top with the meat sauce. Dot with the remaining white sauce and mozzarella; bake for 20-25 mins until lightly golden on top and gently bubbling. Serve with a side salad.
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For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home.