Season the steaks with salt. Coarsley grind the peppercorns in a coffee grinder. With a small knife, spread a tablespoon of mustard on one side. Pack the pepper into the steak. Turn the steaks over and spread another tablespoon of mustard. Pack the pepper into the steak on the second side. Heat the oil in a large skillet over medium heat. Add the steaks and sear for 4 to 5 minutes on each side. Remove the steaks from the pan.
Using a mandoline fitted with a waffle blade, cut the potatoes thinly, in a crisscross motion, to form a waffle-like chip. Fry in hot oil until golden brown, about 4 to 5 minutes, stirring occasionally for overall browning. Remove and drain on paper towels. Season with salt and set aside.
Add the shallots and garlic, and cook, stirring, for 15 seconds. Carefully add the brandy and flame. Add the demi-glace, cream and mustard. Mix well. Bring the liquid to a simmer and cook for 1 minute. Add the steaks back into the pan and continue to cook for 1 minute on each side. Remove the steaks and place in the center of each plate. Stir the parsley into the sauce and spoon on top of each steak. Serve each steak with a pile of the waffle chips.
Yield: 4 servings