Bring beef to room temperature. Pat it dry and season liberally with salt and pepper.
Chop the bacon into a 1/4-inch dice.
Gently wipe mushrooms clean with a damp towel then cut into quarters or slice them.
Preheat a cast-iron skillet over medium-high heat. Add enough oil to coat pan lightly then add steaks. Cook about 3 minutes on each side until crusted and well-browned; remove to a platter.
Add bacon to pan and render 2-3 minutes. Add mushrooms and brown. Add shallots and garlic, and season with salt and pepper. Stir 2 minutes more then add sherry or wine, and scrape up drippings.
Serve steaks on a plates or platters with mushrooms alongside.