Make this for Martha's Meyer Lemon Anniversary Cake.
Heat sugar, zest, and 2 cups water in a small saucepan over medium-high heat, stirring, until sugar has dissolved. Bring to a boil. Pour through a fine sieve into a medium bowl; discard solids. Let cool completely. Stir in lemon juice.
Syrup can be refrigerated, airtight, up to 1 month.