In a small saucepan, bring 1 cup (250 ml) of the cranberry juice and the sugar to a boil, stirring until the sugar has completely dissolved. Remove from the heat. Add the remaining cranberry juice (3 cups/750 ml).
In a large airtight container, combine the cranberry juice mixture, vodka, triple sec and lime juice. Cover and freeze for about 8 hours or until the mixture is firm.
In a food processor, purée until smooth or scrape into icy crystals with a fork. Spoon the slush into glasses. Keep the remaining slush in an airtight container.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.