Season the beef roast generously with salt and pepper.
Place it in a slow cooker.
Add the beef broth and onion soup mix.
Cover and cook on low for about 8 hours, or until the roast is tender.
Once cooked, remove the beef from the slow cooker and set it aside.
Reserve the cooking juices for the gravy.
In a bowl, combine cornstarch and water to form a smooth slurry.
Mix it well to avoid clumps.
Transfer the cooking juices to a pot on the stove.
Bring it to a gentle simmer over medium heat.
Gradually whisk the cornstarch slurry into the simmering juices.
Stir continuously until the gravy thickens to your desired consistency.