I'm still experimenting with sorbets, and the results have been nice. If I made the prune one again, I'd use much less sugar, and perhaps a squeeze of orange or lemon juice, but no matter, both containers will be gone in a day.
For the blueberry/grapefruit:
1 pint blueberries
1 cup water
1 cup fresh squeezed pink grapefruit juice
1 1/2 cups sugar (you can reduce this to 1 if you like)
In a heavy pot, combine the water and blueberries. Bring to a boil and cook until they pop (watch to make sure it does not boil over. Strain into a bowl and then force the blueberries through a fine mesh sieve (this takes some time, but it is nice to not have seeds in your sorbet). Return to pan and whisk in sugar over medium heat. Whisk just until dissolved. remove from heat, chill. When cool, mix with grapefruit juice and begin freezing in a glass or metal pan. The first freeze will take about an hour. Break up any crystals forming around edge with a fork and do this every thirty minutes for a couple hours until it is a slushy, thickened texture. Transfer to a plastic container and freeze several hours.
For the chocolate/prune sorbet:
1 cup water
1 cup sugar (you can reduce this to 3/4)
1/4 cup dark cocoa powder
1 cup unsweetened prune juice
Combine waster and sugar in a heavy pot. Whisk over medium heat until dissolved. Whisk in the cocoa until combined. Cool. Stir in prune juice. Freeze following method above.