In a 5 qt or larger crockpot place 1.5 - 2 lbs cubed steak.
Sprinkle with onion soup mix and pour in the beef broth. If desired add 1 cup sliced mushrooms or some diced onion at this step (optional).
Cover and cook on low for 6 hours or high for 2.5 to 3 hours.
After cooking, in a small bowl, whisk together cornstarch and cold water. Uncover crockpot and whisk in the cornstarch mix. Turn the crockpot up to high and cook uncovered for an additional 30 minutes or until the gravy is thickened.
Serve with mashed potatoes and veggies.
Use a gluten free beef broth and gluten free onion soup mix. The homemade onion soup mix linked in the recipe is gluten free!