2 teaspoons unflavored gelatin powder
2 tablespoons cold water
1 pound fresh cranberries
2 cups water
2 cups white sugar
2 cups ginger ale
2 (2 liter) bottles ginger ale, chilled
Sprinkle the gelatin over 2 tablespoons cold water and set aside.
Combine the cranberries and 2 cups water in a saucepan over medium-high heat, bring to a boil and cook until cranberries burst. Remove from heat and stir in sugar until dissolved; mix the softened gelatin into the hot cranberry mixture. Pour the cranberries into a shallow freezer-proof container and chill until cold.
When cooled, mix in 2 cups ginger ale and place the mixture into the freezer. Freeze until slushy, about 4 hours. Stir twice during the freezing process to break up the ice crystals.
To serve, fill clear glasses 3/4 full with chilled ginger ale, and spoon some of the cranberry ice overtop. Serve immediately.