In a saucepan, bring sugar, 1 cup water, and lavender, if using, to a boil. Add salt and simmer 2 minutes. Transfer sugar syrup to a metal bowl and let cool to room temperature. Strain and discard lavender.
In a blender, purée sugar syrup, blueberries, and lemon juice. Strain and discard seeds and skin. Cover and chill sorbet mixture at least 30 minutes and up to overnight.
Freeze in an ice cream maker according to manufacturer's instructions. Transfer to a freezer-safe dish, cover, and freeze until hard, at least 1 hour and up to overnight.
The recipe is wonderful! Given to me by my brother-in-law (who is a fabulous cook), he recommended using only wild blueberries and ³⁄₈ cup of Spenda and ³⁄₈ cup of sugar. I made it with ¾ cup sugar, and though I am a purist and don't usually like the taste of low-calories sweeteners, I found his suggestion to be much better. Straining the blueberries through a chinois (my new favorite tool) is a must. I can't wait to make another batch!