Spread marshmallow creme or scatter marshmallows over bottom of prepared crust; set aside. In blender, sprinkle unflavored gelatin over cold milk; let stand 2 minutes. Add hot milk; process at low speed until gelatin is completely dissolved, about 2 minutes. Add cream cheese, sugar, cocoa powder and vanila; process at high speed until blended. Gently pour into prepared crust and chill until firm, about 2 hours.