RESERVE 5 wafers for garnish. Finely crush remaining 35 wafers; mix with butter. Press firmly onto bottom and up side of 9-inch pie plate; set aside. Microwave chocolate and cream in medium microwaveable bowl on HIGH 2 min. Stir with wire whisk until chocolate is melted and mixture is well blended. Pour into crust. Refrigerate 30 min. or until firm.
MICROWAVE 2 cups of the marshmallows and milk in large microwaveable bowl on HIGH 1-1/2 min. or until marshmallows are completely melted and mixture is well blended, stirring after 1 min. Refrigerate 15 min. or until mixture is completely cooled. Gently stir in whipped topping. Spread over chocolate layer in crust.
REFRIGERATE 3 hours or until firm. Top with reserved 5 wafers and remaining 1/2 cup marshmallows just before serving.