In a large mixing bowl, whisk together the root beer, milk, pudding mix, and root beer extract. Keep whisking until the pudding thickens, which should take about two minutes. The extract is key—it enhances the flavor and makes the pie taste like a real float.
Once the pudding mixture is thickened, gently fold in the Cool Whip using a spatula. Folding instead of stirring keeps the texture light and fluffy. This step transforms the mixture into a creamy filling that will set perfectly in the crust.
Pour the creamy mixture into the prepared graham cracker crust. Spread it evenly with your spatula to avoid uneven freezing. Place the pie in the freezer for at least 8 hours, or overnight if possible. The longer it chills, the firmer and easier it is to slice.
When you’re ready to serve, take the pie out of the freezer and let it sit for a few minutes so it’s easier to cut. Top each slice with whipped cream and a cherry to give it the authentic root beer float look. Serve chilled and enjoy the refreshing flavor in every bite.