Stir together cornstarch and milk. Bring condensed milk, butter and corn syrup to a boil over medium-high heat in a small saucepan, stirring constantly to prevent burning. Whisk in cornstarch mixture; cook 2 minutes, whisking, or until thickened. Pour over crust, spreading level. Bake at 350 degrees F. for 8 minutes or until topping starts to bubble. Remove to a rack; refrigerate for 2 hours or until cool.