Place leftover pork roast and beef roast in a large slow cooker. Add 2 cups beef stock and onions. Set slow cooker to low and cook until meat is tender to shred with forks. This is about 5 hours.
Take meat out of slow cooker after 5 hours and shred on a separate plate. It is just easier this way. Put back into cooker along with the remaining ingredients.
Cook for another 3 hours on low in slow cooker and enjoy.