In a medium saucepan, heat vinegar over medium-high heat. Allow the mixture to bubble away for 7 - 10 minutes, stirring with increasing frequency. When the mixture has some body – enough to coat the back of the spoon – off the heat, cool for a few minutes, check the viscosity, and serve. If it's too thick, c'est la vie, though it will be loose-est warm; not thick enough, just let it cook down a bit more.

Some people add sugar or honey – you can if you'd like, but I find the sweetness of the reduction is perfect as is.

Save any leftovers in the fridge and reheat before serving.