Microwave chocolate and 2 tablespoons of the milk in large microwave-safe bowl on HIGH 1 1/2 to 2 minutes or until chocolate is almost melted, stirring halfway through heating time. Stir until chocolate is melted and mixture is smooth.
Beat in cream cheese, sugar, and remaining milk with wire whisk until blended. Refrigerate 10 minutes. Gently fold in 3 1/2 cups of the whipped topping until no streaks remain. Spoon into crust.
Freeze pie 4 hours. Before cutting pie, let stand at room temperature 15 minutes. Serve with remaining whipped topping. Store pie in freezer.
