Let the Cube steak come up to room temperature, then sprinkle each with a pinch of salt and black pepper
Heat the oil in a cast iron pan on the stove, then sear the steaks for 1 minute on each side
*If using the mushrooms and/or onion. Saute the mushrooms and onions until they’re starting to brown
Layer the meat (and onions and mushrooms if using them) in a Dutch oven or roasting pan with no rack in it
Use the cast iron pan to melt the butter. When it’s starting to turn slightly brown, mix in the 1/4th cup of flour and the salt, garlic powder, and black pepper. Keep stirring this mixture regularly so it cooks slowly over medium heat until it is a nutty brown color. Whisk in the beef broth a little at a time until you get a smooth gravy
Pour the gravy over the steaks in the roasting pan or Dutch oven
Cook the Cube steaks at 300 degrees F for 2 hours with a lid on the pan, letting the dish rest for 10 minutes before serving