Boil the kettle and finely chop your mint leaves. Place them into a bowl.
Measure the boiling water on top of the mint leaves and stir. They should be just covered. Add the sugar and stir to dissolve it, then either let the bowl cool naturally or place it in the fridge/freezer to do this fast.
Measure in the vinegar and season with salt and pepper to taste.
Notes
I find that apple mint tastes best, but you can use whichever mint variety you can find. You need enough boiling water to just cover the herbs. Use the same amount of vinegar.