Wash the passionfruit thoroughly, then slice them in half and empty the pulp into a bowl. Set aside.
Add the cream and sugar to a pan over medium low heat, and bring to a slight simmer. Add the passionfruit and use a spatula to squeeze out as much of the juice from the pulp as possible. Turn the heat to very low. At this point, if the cream appears to have thickened, you can skip the lemon. If not, add a tablespoon of lemon juice to help it thicken.
Strain this mixture through a sieve. Use a spatula to squeeze out all the juice through the sieve. Allow it to cool a little bit before pouring it into the hollowed-out passionfruit shells. You'll have more filling left over than will fill the shells, which you can serve in little dessert cups.
Refrigerate for at least four hours before serving, but it's best left overnight. Enjoy!
