Melt 1 tablespoon of the butter over medium-high heat in a large skillet. Season both sides of the steaks with salt and pepper and add to the hot skillet.
2 tablespoons butter, 4 4 ounce steaks, salt, pepper
Cook until nicely browned, about 3-5 minutes, then flip and cook an additional 3-5 minutes or until the steaks are done to your preference. Remove to a plate and tent with foil to keep warm.
Return the skillet to the stovetop and add the remaining tablespoon of butter. Add the mushrooms and cook 2-3 minutes, stirring frequently.
2 tablespoons butter, 8 ounces mushrooms
Stir in the shallot, garlic, lemon juice and Dijon mustard. Cook about 1 minute. Carefully add the cognac or brandy, if using, as it may flame while the alcohol cooks off.
1 shallot, 2 cloves garlic, 1 tablespoon fresh squeezed lemon juice, 2 teaspoons Dijon mustard, 2 tablespoons cognac
Pour in the stock and cook an additional minute or two to heat through. Slowly whisk in the cream. Taste as season as desired, if needed.
1/2 cup beef stock, 2 tablespoons heavy whipping cream
Return the steak and any accumulated juices back to the pan. Spoon sauce and mushrooms over the steak and garnish with parsley.
1 tablespoon fresh parsley