Pour over the beef broth and Worcestershire sauce.
Cook on LOW for 9 hours.
While the roast is cooking, make the horseradish sauce by adding the horseradish ingredients in a small bowl and mixing with a spoon. Refrigerate until ready to serve.
When the cooking time is up, shred the meat with 2 forks and discard any fat. You can do this right in the slow cooker or on a plate.
Toast the buns if desired. Strain the meat and place on the buns. Add the horseradish sauce on top of the meat.
Serve and enjoy!
Notes
Add any remaining beef to an airtight container and store in the fridge for up to 4 days. If you're serving this for a potluck, you can cover it with the crock pot top or with a piece of plastic wrap.
If you don't like the spiciness of the horseradish, use less and taste as you add it.
French bread, hoagie rolls or ciabatta rolls can be used instead of hamburger buns.