Heat the olive oil in a very large frying pan or saucepan over a medium-high heat
Fry the sliced onion, stirring occasionally for 5 minutes or until soft
Add the crushed garlic and steak mince and fry for 5 minutes, continuing to stir as the meat browns
Stir in the tomato, beef stock, tomato paste and balsamic vinegar
Bring to a boil before reducing the temperature to a moderate heat and simmering for 15 minutes until the sauce thickens
Cook the pasta in boiling water according to packet instructions, then drain and immediately tip into the frying pan and stir into the ragu
Spoon into warm serving bowls, sprinkle with grated parmesan and serve with fresh salad leaves