A restaurant chef’s secret weapon for mushroom steak sauce is “Demi-Glace,” which is concentrated beef or veal stock that will create a rich, luxurious, meaty flavor that you can’t replicate with any seasoning. Made from scratch demi-glace is a laborious task that takes 4 hours or more of roasting bones and reducing the broth until it becomes thick, syrupy and viscous.
If you prefer to make your own, here is Chef Steps’ recipe, which takes 3-4 hours.
Prep Time: 5 minutes
Cook Time: 10 minutes
If you can't find demi-glace, don't worry, just follow recipe and you'll still get an incredible mushroom sauce to top steak. I like using crimini mushrooms (which are actually baby portobello mushrooms).
Heat the butter in a frying pan over medium heat. Add the shallots and saute for 30 seconds. Add in the mushrooms, and saute for 2 minutes. Add in the broth, wine, cognac and demi-glace. Simmer until sauce is reduced in half and thickened, about 2 minutes. Season with salt and pepper (if using demi-glace, just season with pepper). Sprinkle with chives and pepper just before serving.