Stir together water and sugar in a medium saucepan. Use a microplane zester to grate the zest of one lemon into the saucepan. Heat until sugar is dissolved, stirring often. Pour into a small jar, allow to cool and refrigerate until cold.
Juice the zested lemon and the other lemon and measure out ¼ cup of lemon juice. Whisk together chilled lemon syrup, buttermilk and lemon juice. Pour into ice cream maker and process as directed.
Recipe by Crumbs and Chaos at http://www.crumbsandchaos.dreamhosters.com/2014/06/lemon-buttermilk-sherbet/