Slow Cooker Beef and Broccoli

3 lb. chuck roast

2 cups beef stock

1/2 cup soy sauce

1 tablespoon toasted sesame oil

1/2 cup brown sugar

4 cloves garlic, minced

2 tablespoons rice wine vinegar

2 tablespoons cornstarch

large head broccoli florets

Mix the stock, soy sauce, sesame oil, brown sugar, garlic, and vinegar in the bottom of the slow cooker.  Lightly salt and pepper the roast and place in the the slow cooker with the sauce.  Cook on low for 8 hours.  In the last 30 minutes of cooking,  shred the beef with a fork.  Remove any big chunks of fat.   Remove half a cup of the sauce from the slow cooker.   Add the cornstarch to the reserved sauce and stir. Add the mixture back to the slow cooker, this will thicken the sauce.  Add the broccoli about 15 minutes before serving.  Serve over hot rice.