Add sugar and water to a saucepan. Set the pan over medium heat. Stir gently as the sugar dissolves.
Warm until clear. Bring the mixture just to a simmer. You don’t need a rolling boil—once it’s clear and the sugar is fully dissolved, you’re set.
Add vanilla. If using a vanilla bean: Split it lengthwise, scrape the seeds into the pan, and drop in the pod.
Simmer on low for 2 to 3 minutes to infuse.
If using vanilla extract: Remove the pan from heat first, then stir in the extract to protect its delicate flavor.
Add a pinch of salt. This small step balances sweetness and makes the vanilla pop.
Cool and strain. Let the syrup cool for 10 to 15 minutes. If you used a bean, strain out the pod and any seed bits through a fine mesh strainer.
Bottle it. Pour the syrup into a clean glass bottle or jar. If you used a vanilla bean, you can add the pod to the bottle for extra infusion.
Label and refrigerate. Mark the date and store in the fridge.
It will thicken slightly as it chills.