In a medium saucepan, whisk egg, egg yolks and sugar together until smooth. Whisk the corn starch together with a bit of passionfruit puree to create a slurry. Whisk the rest of the passionfruit puree and the slurry into the egg mixture. Continue to whisk over medium heat until thick, 10-15 minutes. It should be the consistency of pudding. Make sure the whisk hits the bottom of the pot to keep the bottom from burning. This is less likely to happen if you use a heavy-bottomed saucepan.
Over low-heat, slowly whisk in the pieces of butter.
Move the curd to a bowl and allow to chill in the refrigerator. It will continue to thicken as it cools. Lining the top of the curd with plastic wrap will prevent a skin from forming.
Prepare the parfait:
In a small bowl, combine the graham cracker crumbs, melted butter and lemon zest. Set aside.
In a stand mixer with the whisk attachment, combine the heavy cream and cream cheese until they're incorporated. Add the sugar and vanilla and then turn the speed up to high and allow the mixture to reach a stiff peak.
In a decorative glass of your choice, layer the three ingredients : start with the cream cheese filling, followed by the curd, the crumbs and the blueberries. Take care with each layer to make sure it looks relatively level and even, though it doesn't need to be perfect. Finish by garnering the top with a small amount of cream cheese filling and blueberries.