Place the beef in a large dutch oven and top with the bouillon cubes and onion soup mix. Pour the hot water over the top. Bake for 5 hours.
Remove the beef from oven and shred the meat. Pour the juices through a strainer (but saving the liquid) to separate the onion bits . Add the onion bits back to the meat. Put the liquid in a separate container and refrigerate to separate the fat.
When solidified, remove the fat and pour juice over meat to store.
To serve: Reheat in oven at 300 degrees for an hour or until heated through. Make sure you cover pan with aluminum foil to keep moisture in. Alternatively you can reheat in slow cooker on low for 2-3 hours.