Pour the balsamic vinegar, garlic (if using), and honey into a small saucepan over medium heat. Stir well to combine the ingredients.
Bring the mixture to a light boil, then lower the heat to maintain a gentle simmer. Let it cook for 10-20 minutes, stirring occasionally, until the liquid is reduced by half and becomes syrupy.
Remove the saucepan from the heat and let the glaze cool. The glaze will thicken further as it cools. Once cooled, pour it into a clean glass jar for storage.