Bring the stock to a simmer. Heat a large wide pan and add half the butter and the olive oil. Add the spring onions, leeks and garlic and cook for 5 minutes until softened. Add the rice and stir to coat then tip in the wine and bubble until reduced. Add the stock a little at a time, stirring until the rice is tender with a little bite and oozy. Stir in the parmesan and the rest of butter and season.