Set aside 1 tablespoon of chocolate cookie crumbs for garnish, or as desired. Combine remaining cookie crumbs with butter in a bowl; press into the bottom of a deep-dish 9-inch pie plate.
Heat marshmallows and milk in a large saucepan over low heat, whisking until marshmallows melt. Marshmallows will inflate and rise to the top of the pan as they heat; stir constantly to avoid boiling over. Cool marshmallow mixture to room temperature. Stir creme de menthe and creme de cacao liqueurs into mixture.
Set pot into a large bowl of ice and chill until marshmallow mixture is cold and syrupy, at least 30 minutes. Gently fold whipped cream into marshmallow mixture. Pour filling into prepared cookie crust. Chill overnight. Sprinkle with reserved cookie crumbs.
The liqueurs in this recipe are not cooked, so you may want to substitute them for a few drops of green food coloring and some mint extract if serving to children.
The pie should be a minty green and have a distinct minty flavor. If you are substituting the liqueurs, I would recommend roughly 10 drops of food coloring, and at least a tablespoon of extract. Also goes great with whipped cream. Garnish with cookie crumbs, bitter chocolate shavings, or sprinkles (optional).