Take steak from the refrigerator and let rest at room temperature for 30 min. Prep all the sauce ingredients and have them at the ready. Salt and pepper generously. Grill to satisfactory doneness. For this large steak it was first seared on the flame and then finished on indirect heating to a temperature of 130F. Remove steak to rest.
While the steak is resting, heat a large saucepan, melt the butter over medium high heat and add the shallots. Cook 3-5 min. until translucent. Then add in the green peppercorns and brandy. Cook until the liquid is almost gone.
Mix together the mustard, lemon juice, zest, and worcestershire sauce and add it into the pan. Stir to combine. Add in the beef stock and cook and reduce until desired thickness. Add more beef stock or water if you cook it down too much. Serve over the steak and serve immediately.