Cranberry Port Cheesecake Topping

In small saucepan, bring cranberries, sugar and water to boil; reduce heat and simmer until saucy and berries pop but still retain shape, about 8 minutes.
Whisk cornstarch into port until dissolved; gently whisk into cranberry mixture and return to boil. Boil until thickened, about 1 minute. Let cool slightly; cover and refrigerate until cold, about 2 hours. (Make-ahead: Refrigerate in airtight container for up to 5 days.)
Spoon about 1/2 cup (125 mL) topping evenly over cake, leaving 1/2-inch (1 cm) border. Refrigerate for 2 hours. Serve with remaining topping as sauce.