Season the filets mignons with salt and pepper; set aside. In a small bowl, combine the demi-glace and water; set aside.
In a large skillet over medium heat, add the vegetable oil 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.
Discard all fat from the skillet. While the skillet is still hot, add the red wine, scraping the bottom of the pan. Reduce by half.
Add the veal stock mixture, bring to a quick boil, then remove from heat and stir in the truffle butter to make a silky sauce.