Cut the steak into cubes and season with a little pepper.
Heat the oil in a large flameproof casserole dish over medium to high heat. Brown the steak and then transfer to a plate. Fry the pancetta in the casserole dish until golden and remove to the same plate as the steak.
Reduce the heat and gently fry the baby onions, carrots, celery, mushrooms and garlic in the casserole dish. Cook the vegetables for 5 minutes before adding the chopped tomatoes, tomato puree, beef stock and bay leaves. Return the beef and pancetta to the casserole dish, place a lid on top and boil, then transfer the casserole dish to a hot oven for 90 minutes.
Meanwhile cut the peeled potatoes in half and place into a saucepan of water. Bring to a boil, reduce the temperature and simmer for 10 - 15 minutes until the potatoes are tender, drain and set aside.
Remove the casserole from the oven, remove the lid and discard the bay leaves. Slice the cooked potatoes and arrange on top of the casserole, sprinkle with grated Parmesan and return to the hot oven without a lid for 10 minutes until golden.