The meat will be so tender you can cut it with a fork. Soak the clay pot in cold water for 10 minutes. Tie the beef with string in four places so that it will retain its shape as it cooks. Combine all the marinade ingredients in the clay pot. Marinate the beef for at least 24 hours, turning the beef several times. Add sufficient water or beef broth to the marinade to cover 0.75 of the height of the beef. Place the pot in a cold oven. Adjust the heat to 230ºC . Bake for 1.5 hours. Serve with horseradish.