Cut open the passion fruit, scoop out the flesh and add it to the cocktail shaker.
Measure in the vodka, passion fruit liqueur and freshly squeezed lime juice to the cocktail 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 to see if you need to add sugar syrup (this will depend on the sweetness of your passion fruit). If required, add a ½ ounce measure of sugar syrup and shake again.
Use a fine mesh cocktail strainer to strain the cocktail into a coupe or martini glass.
Garnish with a half passion fruit floating on the surface and a shot glass of chilled champagne or sparkling wine on the side.
Notes
I personally find this drink sweet enough without the added sugar syrup. However, this will depend on how sweet your passion fruit is. I recommend tasting the cocktail before adding the sugar syrup.