Slice the onion into 1/4" rings and layer the bottom of the crock pot. Trim the roast of visible fat, then salt both sides of the roast. Place on top of the onions. 

Add the remaining ingredients to the slow cooker, pouring the broth and soy sauce over the beef. If the roast isn't covered, add enough water ( or more beef broth) to almost cover the meat in liquid.

Cover and cook on high for 4-6 hours or low 10-12 hours. Remove the meat from the liquid. Let stand 5 minutes before slicing thinly across the grain.Serve the meat in a sandwich with a small cup of the au jus to the side.Enjoy!