Prepare an ice-water bath; set aside. Stir together sugar and 1 cup water in a medium saucepan. Bring to a boil, stirring until sugar has dissolved. Remove from heat. Pour into a metal bowl set over ice-water bath. Let cool completely, stirring occasionally.
Whisk in buttermilk, cream, corn syrup, salt, and vanilla seeds (reserve vanilla bean for another use). Freeze in an ice cream maker according to manufacturer's instructions. Transfer to an airtight container; freeze at least 1 hour (up to 3 days) before serving.