Heat the butter in a casserole over medium high heat. Add the beef and brown lightly on all sides. Add the onions and cook until softened. Pour in the stock, seasoning and Maggi (if using) and bring to the boil. Cover, reduce to a gentle simmer and cook for about 1 hour, or till beef is tender.
Mix the cornflour with a little water to make a slurry. Add the mixture to the simmering beef and stock. Stir well and allow to simmer until thickened.