Preheat the oven to 450F. Using a sharp knife, score the steaks in a cross pattern at 1/2 inch intervals, cutting just less than halfway through depth. Preheat the grill to very hot.
Mix together the Woeber’s Reserve Whole grain Dijon Mustard and olive paste and spread over the meat and into the cuts.
Place the steaks, mustard side down, on a foil lined baking tray. Cook under the grill for about 3 minutes on one side only.
Put the mushrooms, flat side up, on the baking tray. Turn the steaks over and carefully place on top of the mushrooms. Bake in the oven for 10 minutes or until the mushrooms are cooked through. (For well done steaks cook for 4 to 5 minutes longer.) Serve immediately