Prepare the croutons and set aside.
Combine the shallots, garlic, port, and tomatoes in a saucepan and bring to a boil. Lower the heat and simmer for 2 minutes. Add 1 teaspoon of the salt, 6 turns of the pepper, and the stock, and bring to a boil. Cook over high heat for 6 minutes.
Meanwhile, sprinkle the foie gras with 1/2 teaspoon of the salt, spreading evenly on both sides of the each slice. Heat a large heavy skillet over high heat until very hot. Add the slices of foie gras and sear until brown, for 30 to 45 seconds on each side; don't overcook! Remove the foie gras to paper towels and reserve the fat left in the skillet.
When the sauce has cooked for 6 minutes, stir in the green onions, vinegar, and truffles. Stir in the reserved fat from the skillet and cook for 3 minutes. Turn off the heat. Makes 1 cup.
Heat the oil in the same skillet over high heat. Add the greens and the remaining 1/2 teaspoon salt and the remaining 6 turns pepper and wilt the greens, tossing, for about 60 seconds. Remove from the heat.
To serve, place 1 crouton on each of 4 plates and top with 1 slice of foie gras. Divide the greens into 4 servings and arrange around the foie gras. Spoon 1/4 cup of the sauce over each slive of foie gras.
Yield: 4 first-course servings