Finely crush the chocolate cookies in a food processor or blender. Mix in the melted butter until evenly combined. Press the mixture into the bottoms and up the sides of a deep dish pie plate and chill for at least 30 minutes.

Meanwhile, melt the marshmallows and milk together in a double boiler, stirring frequently. Once melted, remove from heat, stir in chopped milk chocolate until smooth, and allow to cool.

Whip the cold heavy cream to stiff peaks using a stand mixer or hand beaters. Fold the whipped cream into the cooled chocolate mixture until well combined.

Pour the chocolate filling into the prepared crust and smooth the top.

Top with fluffy marshmallows and refrigerate for at least 2 hours before serving.