Bring the Balsamic Vinegar and Brown Sugar to a boil on medium high heat in a saucepan. Stir to mix in the sugar.
Reduce heat to medium low and let simmer for 20-25 minutes. Once the mixture reduces by half and coats the back of a spoon. (Check by placing some onto a plate and letting it cool – it will thicken and harden more as it cools down).