1. Pour 2 cups of Dr Pepper soda into a saucepan and simmer over medium heat until reduced by half, resulting in a syrup consistency. Allow to cool completely.
2. For the churn method: Mix the cooled soda syrup with heavy cream, whole milk or half-and-half, granulated sugar, and vanilla extract. Chill the mixture for several hours or overnight.
3. Churn the mixture in an ice cream maker for 20 to 25 minutes until it reaches a soft-serve consistency.
4. Transfer to a freezer-safe container and freeze for 4 to 6 hours to set properly.
5. For the no-churn method: Fold whipped heavy cream into the sweetened condensed milk combined with cooled soda syrup, create a smooth mixture.
6. Pour into a container and freeze for about 4 to 6 hours. Stir occasionally to avoid ice crystals.
7. To serve, scoop the ice cream into a glass, pour over freshly opened Dr Pepper, and garnish with maraschino cherries or chocolate chips if desired.