In slow cooker whisk together cans of cream of mushroom soup, onion soup mix and 1 cup of your beef broth. Sprinkle meat with salt and pepper and place cubed steak inside and gently submerge inside, then add onions on top.
Cover and cook on low for 6 hours or until tender to your liking. In a bowl combine 1/4 c remaining broth with cornstarch until smooth. 30 minutes before serving lift lid and pour this into slow cooker for an additional 30 minutes or until gravy thickens to your liking.