First, make the crust: In the bowl of a food processor, pulse Oreo cookies to a very fine crumb. Transfer cookies to a medium bowl; add melted butter and stir until mixture is well-combined. Press the mixture evenly and firmly into the bottom and sides of a 9-inch pie plate (use the bottom of a dry measuring cup to press the crust down as much as possible). Transfer pie plate to the freezer to chill the crust while you make the filling.

In a medium saucepan over medium heat, bring milk to a very gentle simmer. Add marshmallows; stir until just melted. Remove from heat; set saucepan aside to cool to room temperature, then transfer saucepan to the fridge until the mixture is fully cool, even slightly chilled.

Remove saucepan from the fridge; whisk in peppermint extract and vanilla extract until combined, then whisk in 1 to 2 drops green food dye, if using. Set aside.

In a separate large bowl using an electric hand mixer, beat heavy cream on high speed until stiff peaks form, about 3 to 5 minutes. Gently fold whipped cream into marshmallow mixture until just combined.

Spoon and spread filling into chilled and set Oreo crust. Cover pie plate with plastic wrap and return to the freezer. Chill pie for at least 3 hours.

Just before serving, top with more whipped cream and chopped Andes mints/Oreo cookies. Serve chilled. Store leftover pie, covered, in the freezer for up to 1 week.