Yes, you can. I advise sweating the onion and browning the beef before adding to the slow cooker to ensure depth of flavour in the meat pie filling. Then add them to the slow cooker pan along with the rest of the ingredients and cook on low for 5 hours. Tip: as the slow cooker doesn't allow for evaporation, use just half of the stock and top up with more only if your pie filling gets too dry.