Mix together the passion fruit juice and the granulated sugar in a saucepan.
Stir frequently as it cooks on medium-high. Continue to cook until the sugar dissolves and the mixture is slightly thickened. Pour into a container and chill in the refrigerator or freezer.
Coat the rim of your glass with the passion fruit syrup, then coat in salt.
Mix together the ingredients for the margarita - including the cooled passion fruit syrup into an ice-filled glass.
Enjoy immediately.
Notes
The syrup will make enough for two cocktails. You can double (or more) the recipe to serve a crowd,, if needed