Bring white wine, shallot and peppercorns to a boil in a medium sauce pan. Simmer about 5 minutes until mixture is reduced by half. Add the beef and chicken stock and boil until reduced to about 2 cups (may take 25 minutes or more). Add whipping cream and cook another 6 minutes or so until it is thick enough to coat the back of a spoon.
(Optional -if you want a thicker sauce, before you add the whipping cream, remove 1/4 cup of stock, transfer to a jar with a tightly sealed lid. Add 1 Tbsp cornstarch and shake vigorously until evenly mixed. Return slurry to the stock mixture and stir until thickened. Add the whipping cream and stir till evenly mixed.)
Heat the grill on high.
Grill steaks over high heat (roughly 400 degrees) about 2 1/2 minutes per side for rare, 3 minutes for medium-rare, about 5 minutes for medium (140 degrees F) or about 8 minutes for medium-well (150 degrees F). The most accurate way to test for doneness is with an instant read thermometer insertedin the side of the steak. You want the finished internal temperature to be about 125 degrees F for rare, 135 for medium rare, 140 for medium and 150 for well-done. BUT...remove steaks from the grill about 5 degrees before the target temperature above. Steaks will continue to cook dring the tenting process.
Tent the steaks and let them rest for about 5 minutes. The temperature will continue to rise during the tenting. Resting allows the juices to re-distribute evenly throughout the meat and not bleed out all over your plate.
Drizzle steak with sauce or pass sauce seperately.