1. Season the filets mignons with salt and pepper; set aside. In a small bowl, combine the demi-glace and water; set aside.
2. In a large skillet over medium heat, melt a third of the truffle butter with the oil and quickly fry the slices of bread until lightly browned on both sides; remove and set aside. Add another third of the truffle butter to the skillet, and sauté the filets mignons over high heat for 4 minutes a side for rare or 5 minutes a side for medium-rare. Remove the filets from the skillet, set aside and keep warm.
3. Using the same skillet and high heat, sauté the foie gras tourchon slices 90 seconds on each side and put 1 slice on each of the filets.
4. Discard all fat from the skillet. While the skillet is still hot, add the Madeira, scraping the bottom of the pan. Add the veal stock mixture, bring to a quick boil, then remove from heat and stir in the remaining truffle butter to make a silky sauce. Season with salt and pepper to taste.
5. On each of two plates, place the croutons in the center and top with the filet mignon and foie gras. Garnish with a slice of truffle on the top. Spoon the sauce over and around. Serve hot.