There are a few weeks out of the year in which our part of the state is close to perfect: The days are warm and the nights still carry a slight chill,...
In a large saucepan, combine the blueberries with 2 cups of water. Crush the berries slightly with a potato masher and bring to a simmer. Simmer over low heat for 15 minutes until the berries start to burst. Strain the juice into a clean saucepan, pressing hard on the solids to extract all of the juice—you should end up with about 2 1/2 cups of juice. Discard the solids.
Add the sugar and lemon zest and bring the mixture to a boil, stirring to dissolve the sugar. Reduce to a simmer and cook until the mixture thickens, about 20 minutes. Stir in the lemon juice and let the syrup cool. Discard the lemon zest before pouring the syrup into clean bottles or jars. Seal and refrigerate for up to 6 months.