Preheat your oven to 400°. Line a small baking sheet with parchment paper (or foil) and set aside.
Dry the roast with paper towels and sprinkle with sea salt and fresh ground pepper.
Heat a sauté pan and add butter with a splash of olive oil, when melted and hot add the roast and brown on both sides. Set onto prepared baking sheet with parchment, roast for approximately 30 min. Use a meat thermometer to accurately gauge cooking time & temperature. Remove the roast from the oven when the temperature reaches 130°, loosely tent with foil while you make the sauce.
Add the pan drippings, splash of olive oil, mushrooms, chopped shallot to the pan drippings and sauté until translucent.
Stir in flour until well blended; add the red wine, broth and demi-glace.
Simmer until reduced by about by half. Add 2 tablespoons unsalted butter and season with salt and pepper to taste. Pour the sauce into a serving dish such as a gravy boat.
Slice the tenderloin after it has rested for at least five minutes.
This cut of meat can be called a filet mignon roast or chateaubriand
Demi-glace can be found at Gelson's, Lazy Ares and Bristol Farms