Step 1

Arrange a rack in the middle of the oven and heat the oven to 400°F. Let 2 pounds chateaubriand sit at room temperature while the oven heats.

Step 2

Season the beef all over with 2 1/2 teaspoons kosher salt and 1 teaspoon black pepper.

Step 3

Fit a wire rack inside a rimmed baking sheet. Heat 1 tablespoon neutral oil in a large cast iron skillet or frying pan over medium-high heat until shimmering. Add the beef and cook, turning every few minutes, until the outside is evenly browned, 8 to 12 minutes total. Transfer onto the rack. Set aside the pan without cleaning it, you will use it to make the pan sauce later.

Step 4

Roast the beef until an instant-read thermometer inserted into the thickest part registers 115° F for medium-rare or 125°F for medium, 18 to 22 minutes. It’s helpful to start checking the meat early, after about 16 minutes, and check in more than one part of the roast. Remove from the oven, tent loosely with aluminum foil, and let rest for 10 minutes. Meanwhile, prepare the pan sauce.

Step 5

Mince 1 medium shallot. Pick the leaves from 2 sprigs fresh parsley and finely chop until you have 1 tablespoon.

Step 6

Add 2 tablespoons unsalted butter to the reserved pan and melt over medium heat. Add the shallots with 3 fresh thyme sprigs and cook until the shallots are softened, 1 to 2 minutes. Pour in 3/4 cup dry red wine and scrape up any stuck bits on the bottom of the pan with a wooden spoon. Simmer until slightly reduced, 3 to 4 minutes. Add 1/2 cup demi glace and stir to combine. Simmer until slightly reduced, 3 to 4 minutes more. Remove from heat and pour through a fine-mesh strainer into a serving bowl.

Step 7

Remove any butcher’s twine from the roast if needed and cut crosswise into 1/2-inch thick slices. Garnish with the parsley and serve with the pan sauce.