"It used to be the custom to cook Yorkshire Pudding and the Roast Beef in the same pan. Although it is rarely done today, Yorkshire Pudding still taste best if it is cooked in the fat that the meat has been cooked in, so that it absorbed with meat juices. Serve with Horseradish Sauce." Preheat the oven to 450F. Place the beef fat side up in the roasting pan and coat with oil. If you like your beef rare, it should cook for 1 1/4 hours and the meat thermometer should register between 130F and 140F. If you prefer it medium to well done, it should cook for 1 1/2 hours and a meat thermometer should register between 150F and 160F. Baste the meat frequently while it is cooking. Meanwhile, prepare the batter for the Yorkshire Pudding. Sift the flour and salt into a mixing bowl. Make a well in the centre and add milk and the water gradually, beating well after each addition with a wooden spoon. In a separate bowl, beat the eggs until fluffy. Add them to the flour mixture. Beat until bubbles rise to the surface. Pour the batter in a pitcher and refrigerate for 1/2 hour. When the meat is cooked, remove it from the pan and place it on a warm platter. Cover with aluminum foil and let it stand 25 minutes before carving. Reheat the batter and pour it quickly into the still hot cooking pan. Bake it in the oven for 10 minutes at 450F. Then reduce the heat to 350F and cook it an additional 15 minutes, until it is well risen and has turned a golden brown. (Do NOT open the oven door while it is cooking.) Serve immediately from the pan in which it has been cooked. SERVES:6-8