Place the chocolate sandwich cookies in a food processor and pulse until you have fine crumbs. Alternatively, seal the cookies in a zip-top bag and crush with a rolling pin until the crumbs are very fine, almost like sand.

In a medium bowl, stir together the cookie crumbs, melted butter, granulated sugar (if using), and a pinch of fine sea salt until evenly moistened and the mixture clumps when pressed. Pour into a 9-inch pie dish and press firmly across the bottom and up the sides, using the bottom of a measuring cup to compact the crust.

Place the pie crust in the refrigerator for at least 20 minutes while you prepare the filling. For a slightly firmer crust, chill it in the freezer instead during this time.

Add the mini marshmallows and whole milk to a medium saucepan. Warm over low heat, stirring often, until the marshmallows are completely melted and the mixture is smooth and glossy. Do not let it boil.

Remove the pan from the heat and let the marshmallow mixture cool for 5–10 minutes, stirring occasionally. Stir in the green creme de menthe, white creme de cacao, peppermint extract, vanilla extract, a pinch of fine sea salt, and green food coloring if using. Taste carefully and adjust the peppermint extract by a drop or two if needed.

Pour the mint marshmallow mixture into a large mixing bowl and let it cool to room temperature, about 20–25 minutes. It should be cool enough that it will not melt the whipped cream but not so cold that it begins to set.

In a separate large, chilled bowl, whip the cold heavy whipping cream with an electric mixer on medium-high speed until medium-stiff peaks form. When you lift the beaters, the cream should hold its shape, with just the tips curling over slightly. Do not over-whip.

Using a rubber spatula, gently fold one-third of the whipped cream into the cooled mint marshmallow base to lighten it. Then fold in the remaining whipped cream in two more additions, using a gentle scooping and turning motion to avoid deflating the mixture. The filling should be smooth, thick, and fluffy, like a light mousse.

Pour the creamy mint filling into the chilled chocolate cookie crust and smooth the top with a spatula. Cover the pie tightly with plastic wrap or foil. For a soft, creamy texture, chill in the refrigerator for at least 4 hours or until set. For a firmer, frozen pie, freeze for at least 4 hours or overnight.

Just before serving, garnish the pie with whipped cream swirls, shaved dark chocolate or mini chocolate chips, and/or crushed chocolate cookies as desired. For clean slices, run a sharp knife under hot water, wipe dry, and cut, repeating between slices.