1/2cuppowdered sweetenersugar or erythritol or honey. I used Swerve Sweetener
In a medium heavy pot over medium heat, bring blackberries, water and sage leaves to a boil. Let simmer 15 minutes, then crush berries with a wooden spoon. Let sit 30 minutes to steep.
Transfer berry mixture to a strainer over a medium bowl and let drain, pushing on solids to release as much of the juices as possible (if your mixture is very thick and syrupy, add a little water and mix it around to get more of the juices). Discard solids
Whisk in Greek yogurt and sweetener. Refrigerate mixture until chilled, at least one hour.
Stir in vodka.
Pour into canister of an ice cream maker and churn according to manufacturer's directions.
Once churned, transfer to an airtight container, press plastic wrap flush to the surface and freeze until firm but not rock hard, about 2 hours.
Serves 6. Each serving has about 6 g of carbs (this is an estimate based on how many berries I used and how much juice I got out of them).