Season both sides of the cube steak evenly with the sea salt and black pepper.
Heat the ghee in a large cast-iron skillet over medium-high heat until shimmering.
Place the steak in the skillet and sear for 3-4 minutes per side until a golden-brown crust forms and it is cooked through.
Remove the steak from the pan and set aside on a plate to rest.
In the same skillet, add the sliced mushrooms and diced onions, sautéing for 5 minutes until the onions are translucent and mushrooms are tender.
Stir in the minced garlic and fresh thyme, cooking for 1 minute until highly fragrant.
In a small bowl, whisk the arrowroot powder into the cold beef bone broth until no lumps remain.
Pour the broth mixture into the skillet, stirring constantly as it simmers for 2-3 minutes until the gravy reaches a velvety consistency.
While the gravy thickens, steam the green beans in a separate pot for 4-5 minutes until bright green and tender-crisp.
Plate the steak and pour the mushroom gravy generously over the top, serving the steamed green beans on the side.