To cook the filling on the stove, follow the instructions until the cabbage and tomatoes have been added to the meat (but use a large saucepan rather than a pressure cooker). You should also add an extra cup of stock to allow for evaporation. Cover the pan with a lid and bring it to the boil. Reduce the heat to a simmer and leave for 40 minutes (or until the meat is almost tender). Keep your eye on it, if it starts to boil dry, top it up with extra stock. Add the potatoes and carrots and continue to simmer for approximately 25 minutes until the potatoes and carrots have softened. Thicken the gravy with a mixture of cornflour and water if necessary.