Wet the rim of a chilled martini glass with vodka. Place sparkling sugar on a plate, rub the edge of the glass with sugar to coat. Taste your blueberry juice to see how sweet it is. Add ice,vodka, blueberry juice & sweetener (if needed) to a martini shaker. Shake & strain into sugar rimmed martini glass. Float fresh blueberries on the top of the cocktail.