Heat the balsamic vinegar: In a saucepan over medium heat, pour in the balsamic vinegar. If using a sweetener, add it now and stir to combine.

Simmer and reduce: Bring the vinegar to a gentle simmer, then lower the heat to maintain a slow, steady simmer. Let it cook, stirring occasionally, until the liquid reduces by about half. This usually takes around 30 minutes. The glaze should coat the back of a spoon but still be pourable.

Check consistency: Remember that the glaze will continue to thicken as it cools. If it gets too thick, you can thin it out with a splash of additional balsamic vinegar.

Cool and store: Remove from heat and let it cool completely. Transfer to an airtight container or a squeeze bottle for easy drizzling. Store in the refrigerator or cupboard.