Preheat the oven to 425°F.
Rub the olive oil over the beef, and season generously with salt and pepper. Place in a roasting pan and roast until a meat thermometer inserted into the thickness part of the tenderloin reads reads 125 – 135°F for rare to medium rare, or up to 140°F, for medium, about 30 – 40 minutes. Be careful not to cook your tenderloin above 140°F, as it will become dry. Remove from the oven, cover with foil and allow to rest for about 10 minutes to allow the juices to redistribute.
While the tenderloin roasts, melt the butter in a medium saucepan over medium heat. Add the shallot and saute until softened and lightly golden, about 8 – 10 minutes. Add the wine and simmer until it is almost completely reduced. Add the stock and simmer until the sauce reduces and thickens slightly, about 10 minutes longer. If you find your sauce is not thickened to your liking, you can add a slurry of cornstarch and water at this point (see cook’s note). Remove from the heat, and add the diced truffle and season with salt and pepper to taste.
Once it has rested, slice the beef into thick 1-inch pieces. Arrange the slices on a plate and drizzle the warm sauce over the beef and serve any extra sauce on the side.
Stocks can vary so it is important to look at your sauce and decide whether you need to thicken it with a mixture of cornstarch and water. If you find that the sauce is too thin, whisk together 1 teaspoon of cornstarch and 2 tablespoons of cold water in a small bowl until smooth. Stir the mixture into the sauce and allow the sauce to simmer over medium heat, stirring continuously, for at least 5 minutes and until thickened.