Scoop the flesh from four of the passion fruit halves into a cocktail shaker. Add the lemon juice, egg white, spirit and syrup and shake vigorously until frothy.
Add the ice, then shake again until the outside of the shaker feels cold. Double strain into martini glasses (see tip below).
Top up the martinis with the grape juice and garnish with the remaining passion fruit halves.
How to double strainTo ‘double strain’ means to cover the cocktail shaker with a hawthorne strainer (or use the integrated strainer if you have a cobbler-style shaker) while holding a fine sieve over your glass and pouring the liquid through it. The first strainer holds back the ice, while the second, finer strainer gets rid of any smaller bits, such as pips.