Place the graham crackers in the bowl of a food processor and process until you get fine crumbs. (This can also be done in a large plastic zip-close bag with a rolling pin.) Pour the crumbs into a large bowl. Add the melted butter and stir until evenly mixed.
Press the crumb mixture into a 9-inch pie plate, gently packing them so they're firm and in an even layer. If you go up and over the sides, that is fine. Bake the crust for 5 minutes; let it cool and then chill for 20 minutes.
For the filling: In the bowl of an electric mixer fitted with a whisk attachment, add the cream and confectioners' sugar and whip until firm peaks form.
Meanwhile, in a large bowl, whisk together the root beer, milk, pudding mix and root beer extract until thick, about 2 minutes. Using a rubber spatula, gently fold 2 cups of the whipped cream into the root beer mixture until almost completely blended. Pour the filling over the chilled crust and smooth out with a spatula. Top the pie with the remaining whipped cream.
Garnish with maraschino cherries and chill for at least 2 hours. Enjoy!