10oz frozen blackberries
1/2 cup lime juice
2/3 cup sugar
1 liter ginger ale
De-frost the berries in the microwave. Puree in a blender. Pour through a fine metal sieve to get rid of the seeds and other fiber. You should have around 1 cup of blackberry juice.
Stir all ingredients together and chill.
You can dilute it with more ginger ale if desired.