To prepare your margarita glass
Coarsely grind some salt onto a plate or shallow bowl.
Coat the rim of the glass with lime juice (you can use a quarter of lime, or just use the shell of the lime you just squeezed for lime juice).
Dip the rim of the glass into the salt, rotating as you go, until it is fully coated.
To make the margarita
Cut open the passion fruit, scoop out the flesh and add it to a cocktail shaker.
Measure the Tequila, Cointreau and lime juice into the shaker.
Half fill the cocktail shaker with ice cubes. Tightly secure the lid and give it a good shake for at least 10 seconds.
Taste the margarita. If you want it to be sweeter, add the sugar syrup / agave syrup and shake again.
Fill your prepared margarita glass with ice cubes and use a fine mesh cocktail strainer to strain the margarita over the ice.