Season the steaks on both sides with salt and pepper. Rub with olive oil. Heat a heavy skillet – preferably cast iron – over high heat. Add the steaks and cook 4-5 minutes per side, or until cooked to your desired level of doneness. Remove from the pan and tent with foil; let rest while you cook the mushrooms.

Return the pan to medium heat. Add the butter and oil and let melt together. Add the garlic and cook 1 minute, or until fragrant. Whisk in the miso.

Add the mushrooms and cook, stirring frequently, for 5-6 minutes or until the mushrooms are browned and the liquid has reduced to a thick glaze. Stir in the sherry vinegar, scraping up and browned bits from the bottom of the pan. Sprinkle with parsley. Season to taste with salt and pepper.

To serve, slice the steaks across the grain. Top with miso-butter mushrooms.