In a saucepan, combine 1 cup balsamic vinegar and 2–4 teaspoons honey or brown sugar (optional)
Bring to a simmer over medium heat
Reduce heat to low and simmer, stirring occasionally, until thickened and syrupy
Continue reducing until the glaze coats the back of a spoon and you can draw a line through it with a finger
If desired, stir in a pinch of salt and/or 1/2 teaspoon vanilla or 1 teaspoon butter for a smoother finish
Remove from heat and cool to thicken further
Store in a jar in the refrigerator up to 2–3 weeks
To use, drizzle over salads, roasted vegetables, grilled meats, or fresh fruit