Bring sugar and ½ cup water to a boil in a medium saucepan, stirring occasionally, until sugar dissolves. Let cool 5 minutes. Add lemon zest and let sit 30 minutes to steep.
Strain lemon syrup through a fine-mesh sieve into a pitcher; discard zest. Add lemon juice and 3 cups water and stir to combine.
Serve lemonade over ice garnished with lemon slices.
Editor’s note: This recipe was originally published in July 2015.
