In medium sized glass muddle mint leaves with brown sugar, add rum and let it sit for 5 minutes for the rum to infuse with the mint flavour and for the sugar to fully dissolve.
Stir, then add lime juice and scoop the inside of a passion fruit in the glass. Fill the glass with ice, top with soda water and serve immediately.
Notes
Remember to taste the mojito before serving to make sure that the flavours are balanced. Not all mint, passion fruit or lime will release the same amount of flavour, so some adjustment may be needed.