Preheat oven to 180 ° C. Melt 20 g of butter in an ovenproof skillet. Salt beef and brown slightly in pan on both sides; then bake 7 minutes. Remove pan from oven and set hot meat aside.
Put the pan over low heat and deglaze the cooking juices with madeira, letting it evaporate. Add the truffle juice and let it reduce. Add the beef broth and truffles, and season to taste. Bring to a boil and add 10 g of butter. Sauté the foie gras slices in a nonstick skillet and place on the meat.
Put the raisins in a bowl, cover with hot water and let soak 5 minutes; then drain well. Meanwhile, toast the pine nuts.
Melt the remaining butter in another pan and sauté the spinach until it loses its firmness; add the pine nuts and raisins, and season.
Form a bed of spinach on 4 hot plates, arrange the steaks with foie gras, and pour the sauce around the outside.