Melt 1 tablespoon of butter in a large skillet over medium-high heat. Season steaks with salt and pepper, cook for 3–5 minutes each side, tent with foil to keep warm.

Add remaining butter to the skillet, melt, then toss in sliced mushrooms and sauté for 2–3 minutes until softened and browned.

Add finely diced shallot, minced garlic, lemon juice, and Dijon mustard to the skillet. Cook for about 1 minute until shallot is translucent.

Pour in cognac or brandy, allow to flambé, then scrape the bottom of the skillet to deglaze.

Pour in beef stock, raise heat to medium-high and heat for 1–2 minutes, stirring gently.

Whisk in heavy whipping cream and let simmer for another minute or two until it thickens slightly. Season with salt and pepper.

Return steaks to the skillet, spoon sauce over them, let soak for a minute, then serve garnished with parsley.