Place the rump roast in the slow cooker.
Pour in the beer, beef broth, and French onion soup.
Cover and cook on low for 6-8 hours, until the meat is tender and easily shreds.
Remove the beef and shred it using two forks. Return it to the slow cooker to soak up more flavor.
Slice the French bread rolls and spread butter on each half. Toast them in the oven or a skillet until golden.
Pile the shredded beef onto the toasted rolls.
Strain and serve the cooking liquid as a dipping sauce (au jus).
Enjoy your Crockpot French Dip with a side of Broccoli Cauliflower Salad or Caprese Salad Skewers!