In small saucepan, heat oil over medium heat; stir in onion and garlic and cook, stirring occasionally, for 5 minutes or until softened. Stir in port and balsamic vinegar; boil for 5 minutes or until reduced to about 3 tablespoons. Meanwhile, slice cranberries in half; in bowl, stir together cranberries, sugar, salt and pepper. Mix into onion mixture; bring to boil and cook, stirring often for 8 to 10 minutes or until cranberries are tender and sauce is thick. Transfer to nonmetallic containers; store in refrigerator, tightly covered, for up to 1 week, or in freezer for up to 1 month.