Start by chopping the fresh mint leaves.
Take a bowl, put sugar and boiling water in it, and dissolve the sugar.
Add chopped mint leaves, malt vinegar, distilled white vinegar, salt, and garlic to the bowl.
Stir all the ingredients thoroughly.
Let the sauce steep at room temperature for 30 minutes. Or you can refrigerate it overnight to enhance the flavors.
Transfer the sauce to a sterilized glass jar in the refrigerator.
Make sure to finish the sauce within 2 weeks. After that, the taste won't be much better.