Combine 1/4 cup flour, salt and pepper on a flat plate. Coat meat with the flour mixture. Heat large pan with oil and brown the beef.
Place onion and celery in slow cooker, then pour in the liquid stock and top with roast (cut roast in half if it's unable to fit),.
Cover and cook on low setting for 8-10 hours. Depending on how well you enjoy the beef.
Remove beef from the slow cooker and allow to sit until you make the gravy (about 10 mins).
To make gravy pour all the juices from the slow cooker into a pot and puree with a hand wand. Put the meat juices on a very low heat on the stove top. In a separate bowl mix flour and water until liquid paste. Slowly add the flour and water mixture into the gravy pot, mix the gravy until it thickens.
Slice beef and serve with roasted root vegetables and gravy.