Serve this glaze as a dip for Kale Crisps.
Bring vinegar to a boil in a small heavy saucepan; reduce to a simmer, and cook until thickened and syrupy, about 15 minutes. Remove from heat; stir in honey (if desired) and salt. Let cool completely before serving (glaze will thicken slightly as it cools).
Glaze can be refrigerated in an airtight container up to 1 week.