Use a 6-quart slow cooker. Place the meat into your slow cooker insert and add the cranberries, potatoes, and onion. Sprinkle with salt and pepper and stir in the beef broth. Cover and cook on low for 8-10 hours, or on high for about 6 hours. If desired, mash the potatoes with a handheld immersion blender or potato masher to naturally thicken the broth.