Add the butter, diced onions, and garlic to the slow cooker and cook for 3-4 minutes on medium-high heat until translucent.
Add the cubed steak and sear the meat for 5 minutes until browned. Add the beef broth, and gravy mix and season with a pinch of salt and pepper. Whisk until well combined, then cover and cook on HIGH for 3 hours or on LOW for 6 hours.
Once the meat is soft, serve over mashed potatoes and garnish with fresh parsley. Enjoy!