2 cups Balsamic vinegar
Use a heat diffuser when reducing balsamic vinegar. If you boil it too hard the acid will remain and make the glaze too sharp.
Heat the vinegar in a heavy medium saucepan over medium heat until you see steam rising from the vinegar. Decrease the heat and reduce the vinegar for two to three hours until it is thickened and is like a syrupy glaze (like maple syrup). You should have about 1/2 cup of the glaze. Store glaze in a plastic squeeze bottle and bring to room temperature when needed.