Instructions:
- Prepare Ingredients: Rinse the rosemary sprigs gently. If using zest, remove a thin strip using a vegetable peeler, ensuring no bitter white pith is included.
- Combine Base: Add the water and sugar to the saucepan. Place over medium heat.
- Dissolve Sugar: Stir constantly until the sugar is completely dissolved and the mixture is clear. Do not allow it to come to a rapid boil at this stage.
- Infuse Aromatics: Once clear, immediately add the rosemary sprigs (and lemon zest, if using). Gently bring the mixture to a very gentle simmer (just a few lazy bubbles).
- Steep (The Key Step): Remove the saucepan from the heat immediately. Cover the pan and allow the rosemary to steep for 15 minutes. Taste test after 10 minutes; you are aiming for fragrant, not overpowering.
- Strain: Pour the syrup through the fine-mesh sieve into a clean bowl or measuring cup, discarding the rosemary and zest.
- Cool & Store: Allow the syrup to cool completely to room temperature before transferring it to an airtight container or bottle. Refrigerate for storage.