Place the blueberries in a small sauce pan. Over the blueberries pour agave nectar, pinch of salt, and vanilla extract. Stir and place the blueberry mixture on the stove and bring to a simmer over very low heat. Cook until the blueberries soften, about 15-20 minutes.Stir in the lemon juice and vodka and allow to cool completely.
If you wish, puree the blueberries and their liquid in a blender or food processor until smooth, then press the mixture through a strainer to remove the fruit pulp**. Transfer the pureed mixture to an airtight sealed container and chill the mixture thoroughly, preferably overnight.
When the mixture is thoroughly chilled, fold in the heavy cream, and then freeze in your ice-cream making according to manufacturer’s instructions. This makes about a quart of sherbet – And should last in an airtight sealed container for about a week.
** I wanted whole blueberries in my sherbet, so I didn’t puree the mixture. I just strained it a bit and added blueberries that remained whole.