Combine sugar and 2 cups water in a medium saucepan. Stir over medium heat until sugar dissolves completely, about 10 minutes. Increase heat, and bring just to a boil. Let cool.
In a large bowl, combine sugar syrup with buttermilk and vanilla. Transfer the mixture to an ice-cream maker, and follow manufacturer’s instructions to freeze. When freezing is complete, transfer sorbet to an airtight container, and place in freezer for at least 1 hour. Sorbet will keep, frozen, for up to 2 weeks.