Heat: Set a small saucepan over medium heat and add lemon juice, honey, sprigs of thyme, and lemon zest. Cook for 3 to 5 minutes, stirring frequently, until sugar has dissolved. Fish out the sprigs of thyme; it’s okay if a few pesky leaves remain. Let cool to lukewarm (quicken this up by setting the pan in a sink full of cold water).
Freeze: Mix buttermilk into mixture and pour into molds, leaving a little space at the top for them to expand. Insert sticks and freeze until hard (at least 4 hours).
Serve: Run the mold under warm water for a few seconds to loosen them up, then remove from the mold.