2 large Yukon Gold potatoes, diced
8 tablespoons extra virgin olive oil
1 cup finely diced onion
thinly sliced black truffles to taste (at least 3 or 4 slices per person)
1 teaspoon finely chopped garlic
1 cup finely chopped watercress
1 teaspoon lemon juice
salt to taste
1 cup finely chopped Italian parsley
3 to 4 ounces beef tenderloin filets
4 slices of gruyère cheese
paprika for garnish

In a large pot with boiling salted water, cook the potatoes for 6 to 8 minutes or until done. Strain and set aside in a bowl.

In a medium sauté pan heat 2 tablespoons of olive oil over medium heat. Cook the onions, black truffle slices, and garlic for 1 to 2 minutes or until soft. (If truffles cannot be found, use thinly sliced fresh domestic mushrooms instead. In place of the 2 tablespoons of olive oil for sautéing, use a little less and add about a teaspoon of truffle oil.) Transfer sautéed ingredients to a bowl and mix with watercress. Add 4 tablespoons of olive oil, lemon juice, salt, and parsley to truffle mixture. Toss 1/2 of the watercress pesto into the potatoes. Set aside.

Preheat oven to broil or the highest temperature.

Season the beef with salt. In a medium sauté pan heat 2 tablespoons of olive oil over high heat, and sear the beef for 1 1/2 to 3 minutes on each side for medium rare or until desired doneness.

Transfer the beef to a plate and keep warm. Place the potatoes in a baking dish, put the cheese on top, and sprinkle paprika over the cheese. Bake in oven to broil until the cheese melts. Remove the potatoes from the oven and divide onto 4 plates, place the beef on top and garnish with truffle watercress pesto. Serves 4.