Step 1

Place 4 beef tenderloin steaks on a cutting board, remove any twine holding them together if needed, and let sit at room temperature. Meanwhile, prepare the following: Trim and slice 6 ounces mushrooms about 1/4-inch thick (about 2 cups). Halve and thinly slice 1 large shallot. Mince 1 large garlic clove. Finely chop 1/3 cup parsley leaves.

Step 2

Pat the steaks dry on both sides with paper towels. Using a rolling pin or the smooth side of a meat mallet, pound the steaks until about 1-inch thick (for easier cleanup, pound between two sheets of plastic wrap if desired). Season both sides with 1 1/2 teaspoons of the kosher salt and 1 1/2 teaspoons of the black pepper.

Step 3

Heat 1 tablespoon of the olive oil in a large frying pan or cast-iron skillet over high heat until shimmering. Add the steaks and 1 tablespoon of the unsalted butter. Sear until browned on the outside, about 2 minutes per side for medium-rare. Transfer to a plate and tent with aluminum foil.

Step 4

Reduce the heat to medium-high and add the remaining 1 tablespoon olive oil to the pan. Add the shallot and garlic and cook, scraping up any browned bits from the pan with a wooden spoon, until the shallots are slightly translucent, about 2 minutes. Add the remaining 1 tablespoon unsalted butter and mushrooms and sauté until the mushrooms are browned, 3 to 4 minutes.

Step 5

Remove the pan from the heat. Carefully add 1/3 cup Cognac. Return to medium-high heat and cook until reduced by half, about 1 minute.

Step 6

Add 1/2 cup beef stock, 1 tablespoon Dijon mustard, 1 tablespoon Worcestershire sauce, 2 teaspoons tomato paste, 1/2 teaspoon kosher salt, and 1/2 teaspoon black pepper, and whisk to combine. Cook until slightly reduced, 2 to 3 minutes.

Step 7

Add 1/3 cup cream and whisk to combine. Bring to a boil, then reduce the heat to low. Pour in any accumulated juices from the plate of steak and simmer until slightly thickened, about 3 minutes.

Step 8

Return the steaks to the pan and warm through in the sauce, about 2 minutes. Garnish with the parsley.