How to Make It
In a large saucepan, combine the cranberries, sugar, and 2 cups water; bring to a boil. Reduce heat and simmer for 5 minutes. Using a slotted spoon, transfer 3 cups of the cranberries to a large bowl, then strain the remaining syrup into the bowl; let cool.
Add the tonic water, vodka, and lime juice to the cranberry syrup. Serve over ice and top off with a splash of cream soda.