Step 1

Pour root beer into a baking pan and freeze, uncovered, until firm, about 2 1/2 hours. Using a fork, scrape into small shards. Cover, and freeze until ready to use.

Step 2

Puree ice cream and reserved cherry juice in a blender until smooth. Add cherries, and pulse until combined but still chunky. Divide among 6 to 8 glasses, and top each with 2 tablespoons root beer granita.