In large mixing bowl combine the root beer, milk, and root beer concentrate. Sprinkle the vanilla pudding mix over it. Whisk together for 1-2 minutes and then let it sit for 5 minutes so it can thicken.

Fold in the thawed cool whip and mix together until it is combined together well. Pour into the prepared crumb crust and evenly spread it out.

Cover with enclosed lid (the plastic lid from graham cracker crust) and place in the freezer for at least 8 hours or overnight.

Before serving prepare the whipped cream topping (if using). Beat together the heavy whipping cream and powdered sugar in a mixing bowl until thick and stiff peaks form. This will take about 5 minutes. Serve a dollop of whipped cream and a maraschino cherry over top of each piece. Or you can spread the whipped cream topping over top the pie and then cut into slices.

Eat & serve straight from the freezer. Store any leftovers in the freezer.