Melt butter in a sauce pan and sauté shallots until transparent, approximately 2-3 minutes.
Add red wine, preferably something you may be sipping while you are preparing this meal. Don’t use plain old cooking wine, big mistake.
Add mushrooms and cook until tender and wine has reduced to an essence.
Add demi glace and stir (with a whisk if you have one) until combined with the shallots.
Simmer until the sauce has thickened, approximately 8-10 minutes or until it is thick enough to coat a spoon.
Salt and pepper to taste and serve over the steaks (and mashed potatoes if you like).