1 Make Oreo cookie crust: Preheat oven to 425°F. In a bowl, mix crushed Oreo cookie halves and 6 tablespoons of the butter. A small handful of the crumbs should hold together when you squeeze it in your fist. If it crumbles apart, add additional water, 1 tablespoon at a time, until it holds together
Pat into bottom and up sides of 10 inch pie dish. Press firmly with the bottom of a cup to tamp down and compact the crust into the pie dish.
Bake in oven for 5 to 10 minutes; remove from oven and cool completely.
Once cooled, place in freezer to chill.
2 Make marshmallow mixture: In saucepan over medium heat, warm the milk until steaming, but not boiling. Add the marshmallows and stir gently until the marshmallows have melted.
Remove the pan from heat and cool to room temperature, then chill in the fridge until cool to the touch. If you want, you can speed up the cooling process by setting the pan in an ice water bath. (If the mixture is room temperature or warmer, it has a tendency to break when you add the remaining ingredients.)
3 Mix in the liquors and whipped cream: Add creme de menthe and creme de cacao to the cooled marshmallow mixture, and mix well. Add a drop or two of green food dye if desired.
With a hand mixer or a stand mixer, whip the the cream until it forms stiff peaks. Fold the whipped cream into the milk and marshmallow mixture in three separate additions. Continue folding and gently mixing until no more streaks of white remain.
3 Pour into chilled pie shell. Freeze for at least 3 hours or overnight. Serve with a dollop of whipped cream and sprinkle with chocolate shavings, if desired.