Begin by patting the beef tenderloin steaks dry with paper towels and season them with kosher salt and freshly cracked pepper on both sides. Brine in the fridge for about an hour for best flavor.

Heat a large skillet over medium-high heat. Add butter and olive oil, allowing the butter to melt. Add the steaks and sear for about 2 minutes each side until medium-rare. Transfer to a plate and cover with foil.

In the same skillet, add more butter and a drizzle of olive oil. Add the cremini mushrooms and cook for about 6 minutes until golden brown. Set aside.

Return the skillet to medium heat, add chopped shallots, and sauté for 2 minutes. Add minced garlic and tomato paste, cooking briefly, then sprinkle in flour and whisk while adding beef broth until thickened.

Lower the heat, pour in heavy cream, stir, and add sautéed mushrooms. Heat through for 2-3 minutes and adjust seasoning as needed.

Plate the Steak Diane and spoon creamy mushroom sauce over the top. Serve with mashed potatoes or a green salad, garnished with parsley or chives.