Fill a cocktail shaker halfway with ice. Pour in vodka, pineapple or passion fruit juice, simple syrup and lime juice.
Slice each passion fruit in half and use a spoon to scoop out the seeds into the cocktail shaker. Secure lid and shake vigorously for a slow count of 10-15 seconds. It's important to shake well so the passion fruit distributes throughout the cocktail. Strain the passion fruit martini into two glasses and top off with about 1oz each of Prosecco. This is optional – it tastes great without, too. We just like a tiny but of fizz!