Steak Diane is a recipe that focuses on the Diane sauce, a sauce made with Dijon mustard, Worcestershire sauce, brandy (or cognac), and heavy cream.
Generously season steaks with salt and pepper and let them rest at room temperature for at least 30 minutes prior to frying.
Heat a large, non-stick frying pan over medium-high heat and add butter and olive oil. Add steak to the pan and cook 4-5 minutes (for medium-rare) and flip and repeat on the other side. Transfer the steak to a plate and tent with aluminum foil to keep warm. (Cooking time may vary depending on the size and cut of the steaks you are using.)
Reduce heat to medium and add shallot to the pan and cook until translucent (3-4 minutes).
Add brandy to the pan and scrape the pan, loosening the brown bits. Cook 1-2 more minutes.
Add tomato paste, Dijon mustard, Worcestershire, salt, and pepper. Stir to combine, and cook until slightly thickened (about 2 more minutes).
Add beef broth and heavy cream and heat to a simmer. Reduce heat to low and simmer for 6-7 minutes.
Add the cooked steaks back to the pan and spoon the sauce over the top. Serve immediately.