Beef Tenderloin Steaks with Mushroom Sauce

• 6 tablespoons unsalted butter
• 12 ounces mixed mushrooms, coarsely chopped

Kosher salt

Pepper

• 2 cups chicken stock or low-sodium broth
• 2 tablespoons demiglace (1.5 ounces)

Four 6-ounce center-cut beef tenderloin steaks

• 2 tablespoons extra-virgin olive oil

1. Preheat the oven to 450°. In a large cast-iron skillet, melt 2 tablespoons of the butter. Add the mushrooms and cook over moderate heat until golden brown, 10 minutes. Season with salt and pepper. Add the stock and demiglace and bring to a boil. Simmer the sauce until thickened, 10 minutes. Whisk in the remaining 4 tablespoons of butter and season with salt and pepper. Transfer the mushroom sauce to a medium bowl or saucepan and keep warm. Clean the skillet.
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3. Heat the skillet. Rub the steaks with the olive oil and season with salt and pepper. Sear over moderately high heat until browned, about 2 minutes per side. Transfer the skillet to the oven and cook the steaks until an instant-read thermometer inserted in the thickest part registers 125°, 6 to 8 minutes. Transfer the steaks to a work surface and let rest for 5 minutes. Serve the steaks with the mushroom sauce.