3/4 cup Root Beer chilled
1/2 cup milk chilled
3.4 oz box instant vanilla pudding mix
8 oz whipped topping thawed according to package directions, divided
1 pre-made graham cracker pie crust
8 maraschino cherries patted dry
additional whipped cream
Beat root beer, milk, and pudding mix with a hand mixer for 2 minutes. Gently fold in half of the whipped topping. Spread root beer mixture into the bottom of the shortbread crust. Gently spread remaining whipped topping over the root beer layer. Cover and freeze for at least 2 hours. Before serving, garnish with additional whipped cream and maraschino cherries.