Tenderize the cube steaks and season them with salt and pepper on both sides.
In a large skillet, heat the oil over medium-high heat. Sear the cube steaks for about 3-4 minutes on each side, or until they get a golden-brown crust. Remove the steaks from the pan and let them rest.
In the same skillet, add 2 tablespoons of butter and sauté the sliced mushrooms until they're nicely browned. Like the cube steak, remove the mushrooms and set them aside.
Reduce the heat to medium and melt the remaining 2 tablespoons of butter in the same skillet. Add the flour and whisk to create a roux. Cook the roux for a minute or two to remove the raw flour taste.
Gradually pour in the beef broth while whisking constantly to prevent lumps. If this is your first time making a roux, have someone pour the liquid while you whisk. Continue whisking until the gravy thickens, about 5-7 minutes.
Add in the garlic powder and thyme, if using. Let the gravy simmer for another 2-3 minutes to allow the flavors to fully combine.
Return the sautéed mushrooms to the gravy and mix well.
Gently place the seared cube steaks back into the skillet, making sure they're submerged in the gravy. Let them simmer in the gravy for 5-10 minutes to absorb the flavors.
Serve the cube steaks hot, topped with mushroom gravy and a sprinkle of chopped fresh parsley for a burst of color and freshness. You can also serve it on top of white rice or with your favorite side dishes.