Place raspberry chips and milk in large microwave-safe bowl.
Microwave at HIGH (100%) 1 minute or until chips are melted and mixture is smooth when stirred.
Add marshmallows; microwave at HIGH 1 minute; stir. If necessary, microwave at HIGH an additional 30 seconds at a time, stirring after each heating, just until marshmallows are melted when stirred.
Spread 1/2 cup chip mixture over bottom of crust.
Cool remaining mixture to room temperature; fold in whipped topping. Spoon into crust.