Clean and slice up the yellow onion and set aside, this goes on top of the roast.
Lay your carrots at the bottom of your slow cooker and then add the roast on top, your seasoning, onions, and stick of butter.
Turn your slow cooker on low and let it cook for 6-7 hours or until the roast is easily shredded with a fork.
Once the roast is finished shred it on a plate and remove the carrots from the slow cooker.
Put all the drippings in a bowl and add ice cubes. It'll seize the fat up. Spoon out all the fat and ice and use the beef drippings for the sauce.
Add the beef drippings to the pan. Then add the broth, Worcestershire sauce, soy sauce, balsamic vinegar, and brown sugar, and stir until well mixed.
Add the cornstarch and cold water into a separate bowl.
Slowly pour the cornstarch mixture into your balsamic vinegar mixture and mix vigorously until thickened.
Once thickened add the roast beef and carrots into the balsamic mixture and stir until coated.
Serve!