Preheat oven to 150C/300F/Gas 2.
Heat the olive oil in a large casserole dish over a medium heat. Add the beef pieces and cook for 4-5 minutes, stirring occasionally, or until browned all over.
Add the marrow bones to the pan and continue to cook for a further 2-3 minutes.
Remove the beef and marrow bones from the pan and set aside on a warm plate.
Add the chopped onions to the casserole the beef was cooked in. Fry in the pan juices for 1-2 minutes, or until softened.
Stir in the potatoes and swede and continue to cook for a further 2-3 minutes.
Add the chopped leeks, carrots and bay leaves and season, to taste, with salt and freshly ground black pepper. Continue to cook for a further 1-2 minutes, or until just softened.
Return the beef and marrow bones to the casserole, then pour over enough beef stock to just cover the casserole contents.
Cover the casserole with a lid, then transfer to the oven and cook for 2½-3 hours, or until the beef is tender.
To serve, spoon some of the lobscouse casserole into the centre of four to six serving plates and serve with crusty bread, if desired.
