Just AddMarmite

For burgers, shape the meat into 4 8- oz. patties about 1 inch thick. Handle lightly to keep texture and juicy. In a small bowl, stir together cornstarch and about 2 Tbsp. of stock until well blended. Set aside. Heat 2 Tbsp. olive oil in a large skillet over medium-high heat until very hot. Generously season the meat on both sides with salt and pepper. Cook meat on 1 side until brown, about 1 minute. Then turn and brown the second side for about 3 minutes. With a large spoon, baste burgers several times with fat in the pan. Turn again and cook another 3 minutes, occasionally basting, for medium rare. Remove burgers to a warm platter and reserve a cooking skillet. Keep burgers warm and let rest for several minutes before serving.

Working quickly so the skillet is still hot, pour out the remaining fat, and return the pan to medium-high heat. Deglaze with Madeira: cook until reduced to 1 tsp. Add remaining stock and bring to boil. Cook until reduced by about a third, about 2 minutes. Add cornstarch mixture and stir until sauce has thickened about 1 minute.

Split bun and lightly toast. Spread 2 Tbsp. of butter on the cut side of the buns. Set aside.

While burgers are resting, place dry skillet over medium heat until hot. Remove foie gras from the refrigerator and put it directly into the hot pan season with salt and pepper to taste. Cook until browned, about 30 seconds, and turn again. Turn again and cook for 30 seconds and repeat. Foie gras should be brown and crusty on both sides. Be careful not to burn foie gras or fat remaining in the pan. Drain foie gras on paper towels. Set aside and keep warm. Pour fat from the pan into Madeira sauce (if desired).

Heat remaining butter in a skillet over medium heat until butter begins to bubble. Add truffle slices and cook until warm through, about 30 seconds. Set aside and keep warm.

To assemble burgers, put the bottom half of the bun on the plate. Arrange burger on bun and drizzle with sauce. Top each with a slice of foie gras and slices of truffle. Sprinkle lightly with fleur de sel. Balance the top of each bun against the burger and add a few watercress sprigs between bun and burger. Serve immediately.