Trim tenderloin of all fat and sinew. Portion into 6-ounce fillets and tie to keep shape. Set aside.
Potato Puree: Bring the potatoes to a boil in salted water and then reduce to a simmer. Steep the minced black truffles in heavy cream. When the potatoes have fully cooked, drain in colander until dry, but still warm. Push the potatoes in a fine drum sieve or rice into a bowl. Whisk in heavy cream and butter. Finally, add truffle oil and season, to taste.
Red Onion Confit: Sweat the onions in oil in a small rondeau until wilted and tender. Add vinegar and cook until dry. Add sugar, wine, and thyme, and cover. Cook on low heat until the liquid has been evaporated and the onions are very soft. Hold warm in pot with lid.
Red Wine Demi-glace: Simmer wine and aromatics until almost all of the wine has evaporated, being careful not to burn. Add veal stock and reduce to until proper consistency is achieved. Strain through chinois and hold in a small bain marie.
Assembly: Season the buffalo and foie gras on both sides with salt and pepper. Sear the seasoned Buffalo filet in a little oil on both sides until desired temperature is reached. Add seasoned foie fras and cook until just cooked through. Baste meat and foie gras with a little butter and thyme. Drain on paper towel. Place some truffled potato puree in the middle of the plate, place the buffalo on top. Take warm onion confit and place on top of the buffalo followed by foie gras. Spoon warm sauce over the top. Sprinkle with chives and a little truffle oil.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.