1. Prepare and bake pie crust in 9-inch pie plate as directed on package for unfilled 1-crust pie.
2. Place marshmallows and milk in large microwave-safe bowl. Microwave at MEDIUM (50%) 1 minute; stir. If necessary, microwave at MEDIUM an additional 30 seconds at a time, stirring after each heating, until marshmallows are melted and mixture is smooth when stirred. Add chocolate chips; stir until melted and mixture is smooth. If necessary, microwave at MEDIUM an additional 15 seconds at a time, stirring after each heating, just until chips are melted when stirred. Spread 1 cup chocolate mixture over bottom of crust; refrigerate. Cool remaining mixture to room temperature.
3. Beat whipping cream until stiff; gradually blend into chocolate mixture, combining thoroughly. Spread over chocolate layer in pastry crust. Cover; refrigerate 4 to 6 hours or until well chilled. Garnish with sweetened whipped cream and chocolate curls, if desired. Cover; refrigerate leftover pie. 6 to 8 servings.