Pour 1 cup of Dr Pepper into a saucepan and simmer over medium heat for 15–20 minutes, until reduced to about 1/4 cup. Stir occasionally and let cool completely.
In a mixing bowl, whisk together the pudding mix, reduced Dr Pepper, and the remaining 1 cup Dr Pepper until fully combined.
Slowly pour in the half and half while continuously whisking until smooth.
Gently fold in the whipped topping until fully combined.
Spoon the filling into the graham cracker crust and spread evenly.
Freeze for at least 4 hours, or preferably overnight, until fully set.
Top with whipped cream and maraschino cherries before serving, if desired.
Notes
Store the pie covered in the freezer for up to 5 days. If the pie sits out and softens, return it to the freezer until firm before serving again. For best results, slice just before serving and keep any leftovers frozen.
Regular Dr Pepper is required for this recipe, as the sugar is necessary to properly reduce the soda and create the concentrated flavor.
Disclaimer: Nutrition information is estimated based on automated calculations and should be considered as an approximation. These estimates are provided as a courtesy. Please use your own brand's nutritional values to verify accuracy.