OK, so lemon verbena isn't a fruit--but it does add fruity flavor to this lovely dessert. Its floral aroma and taste soften the tang of the buttermilk.
1. Combine first 3 ingredients in a saucepan, stirring until sugar dissolves. Bring to a boil; boil 2 minutes. Remove from heat; let stand 30 minutes. Pour syrup through a fine sieve into a bowl; discard solids. Stir in buttermilk, rind, and salt; chill 1 hour.
2. Pour mixture into the freezer can of an ice-cream freezer; freeze according to manufacturer's instructions. Spoon sherbet into a freezer-safe container; cover and freeze 1 hour or until firm. Garnish with lemon rind strips, if desired.