Cut the pork lengthwise, and lightly slash the meat with a sharp knife. Tie up the two pieces of meat with string to hold their shape while cooking. Crush the leek, garlic and ginger together. A food processor works very well for this. Combine the condiments with the remaining ingredients and mix well. Pour over the pork and marinate in the refrigerator for three hours, using a non-aluminium shallow pan. Turn over the pork occasionally.