For beef: 1/4 cup black peppercorns, crushed 1/4 cup Szechuan peppercorns, crushed One 2 pound rib roast, trimmed of excess fat 4 Tablespoons olive oil, divided
For potatoes: Vegetable oil for frying 4 pounds russett potatoes Kosher salt 4 Tablespoons unsalted butter 1/2 cup parsley, chopped
For sauce: 3 shallots, minced 1/2 cup cognac 2 cups gf beef stock 1/4 cup cream 1-1/2 teaspoon gf dijon mustard 2 Tablespoons unsalted butter Salt and pepper
For beef: Spread crushed black and Szechuan peppercorns on a plate. Coat beef with 2 tablespoons olive oil and then place it on plate of pepper to coat on all sides. Press pepper into meat with your fingers. Set aside.
For potatoes: Peel and cut into 1/2" thick slices. Add 2-3" of oil to a large, heavy skillet over medium heat. When hot, add potatoes in batches and fry until golden brown, about 7-10 minutes. Drain on paper towels and season with salt.
Meanwhile cook beef. In a large, heavy skillet heat 2 tablespoons oil. Season beef with salt and add to pan, browning on all sides. Continue to cook until medium-rare, about 14 minutes in all. Transfer to a plate and cover with foil to keep warm. Let rest for 10 mintues.
For sauce: Drain all but 2 tablespoons fat from skillet. Add shallots and cook over medium heat, stirring frequently, about 2 mintues. Add cognac, scraping up any browned bits in pan and simmer until most of the liquid has evaporated. Add beef stock and simmer until reduced, about 3 minutes. Stir in cream and simmer until sauce is thickened enough to coat the back of a spoon, about 5 more minutes. Strain sauce through a sieve and return to pan. Whisk in mustard and butter; seasoning to taste with salt and pepper.
Finish potatoes by adding 4 tablespoons butter to a large skillet over medium heat. Add potatoes and heat through. Add parsley and season to taste with salt.
To serve; place beef on a platter; arranging potatoes around beef. Serve sauce on the side.