- Untie and unroll pork roast. Pierce both sides of roast with fork; place in large plastic food storage bag.
- Thoroughly combine soy sauce, honey, plum jam, ginger and garlic; pour over roast. Press air out of bag; close top securely. Turn over several times to thoroughly coat meat. Refrigerate 8 hours or overnight, turning bag over occasionally.
- Remove pork from marinade; reserve marinade. Reroll and retie roast.
- Place on rack placed in pan of water. Brush thoroughly with reserved marinade.
- Roast in 325ºF. oven 1 hour and 30 minutes, or until meat thermometer inserted into thickest part registers 150º, brushing several times with marinade. (Cover lightly with aluminum foil during last half hour of cooking time if roast browns too quickly.) Let stand 15 minutes before slicing.
- Meanwhile, combine 1/2 cup remaining marinade and 1/2 cup water in small saucepan. Bring to boil and simmer 1 minute; spoon over roast.