To Make the Potatoes:
1.Peel the potatoes and cut into thick rectangles measuring 2 1/2- by 1/2- by 1/2-inch. Put the logs into a bowl and cover with cold water. Refrigerate for 2 hours.



2.Pour 3 to 4 inches of oil into a deep pot and heat to 300°F as measured on a deep-fat thermometer. Drain the potatoes well, pat them dry and slip them into the oil. Blanch until the potato logs are nearly tender but not browned, 7 to 10 minutes. Scoop the potatoes out of the pot to a paper towel-lined plate.



3.When ready to serve, increase the temperature and heat the oil until it reaches 375°F. Lower the blanched potatoes into the oil and cook until golden and crisp on the outside, about 5 minutes. Scoop the potatoes from the oil and drain on clean paper towels. Toss with the chives, horseradish, salt, and pepper.




To Make the Watercress Salad:
1.Whisk together the mustard and sherry vinegar in a medium bowl. Still whisking, drizzle in the olive oil to emulsify; season to taste with salt and pepper. Before serving, add the watercress and mushrooms and toss with the dressing.




To Make the Beef:
1.Bring a medium pot of water to a boil. Scoop the marrow out of the bones and add the marrow to the pot; discard the bones. Blanch for just 15 seconds, remove from the water, and set aside to cool. Cut the marrow into 1/4-inch cubes, put into a medium bowl, and refrigerate.



2.Melt 1 tablespoon of the butter in a small skillet over medium-low heat. Add the onion, season with salt and pepper and cook, while stirring, until the onion is tender but not browned, 5 to 7 minutes. Pour the vinegar into the pan and let it boil away until no liquid is left. Remove from the heat and set aside to cool.



3.Add the sautéed onion to the marrow and stir in the bread crumbs and parsley, and season with salt and pepper. Cover and refrigerate.



4.Center a rack in the oven and preheat the oven to 400°F



4.Melt 1 tablespoon of the butter with the oil in a large ovenproof skillet over high heat. Season the beef on all sides with salt and crushed peppercorns and add to the pan. Brown for 8 to 10 minutes before turning over and browning the other side for 8 to 10 minutes.

Transfer the pan to the oven and roast for about 15 minutes, or until an instant-read thermometer reaches 135° to 140°F for medium rare, basting every 5 minutes. Remove from the oven and transfer the steak to a warm platter or cutting board to rest while you prepare the pan jus.



6.Preheat the broiler.



7.Pour off all but about 1 tablespoon of the fat from the pan. Add the shallot to the pan and over medium-low heat, cook, stirring, for 3 to 4 minutes; pour in the cognac. Increase the heat to high and cook until all the liquid has evaporated. Add the beef stock and bring to a boil. Boil for 1 minute and then remove from the heat.


Whisk in the mustard, the remaining 1 tablespoon of butter and any meat juices accumulated. Season to taste with salt and pepper and strain the jus through a fine-mesh sieve into a warm sauceboat.Two options are the Joseph Phelps 1997 Napa Valley Cabernet Sauvignon and the 1996 Côte Rôtie Brune et Blonde from Etienne Guigal.


8.Remove the string from the beef. Return the beef to the same skillet and top with the marrow crust. Place under the broiler, for 3 to 4 minutes, until the marrow begins to melt and the bread crumbs brown lightly.

To Serve: Fleur de sel or coarse sea salt. Sprinkle the marrow crust with some salt and cut the steak into 1/2-inch-thick slices. Arrange on a warm platter (or on two warm plates) with a stack or two of crisscrossed potato logs and some greens. Spoon the jus over the meat and serve immediately.

To Drink: Two options are the Joseph Phelps 1997 Napa Valley Cabernet Sauvignon and the 1996 Côte Rôtie Brune et Blonde from Etienne Guigal.