Heat 1 tbsp butter in a skillet over high heat; sear steak 3–4 minutes per side for medium-rare, then set aside.
In the same skillet, sauté sliced mushrooms and minced garlic in remaining butter until golden, about 4 minutes.
Add spinach and cook until wilted, about 2 minutes.
Return steak to pan, season with salt and pepper, and serve hot.
Photo: Andre Davis / Unsplash