To make the pastry, place the flour, butter, salt and icing sugar into a food processor and pulse until it begins to look like breadcrumbs.
Add the milk and egg yolks and pulse again until it comes together as a dough.
Turn the dough out onto a floured work surface and roll out to a diameter 5cm/2inches larger than that a 28cm/11inch tart case. Push the pastry into the base of the tart case, leaving excess hanging over the sides, and transfer to the fridge to chill for at least 30 minutes.
Preheat the oven to 180C/350F/Gas 4.
Line the chilled pastry case with aluminium foil and cover with rice or baking beans. Transfer to the oven to bake for 20 minutes, then remove the rice or beans and foil. Brush the pastry with the egg wash and return to the oven to bake for a further ten minutes, until golden brown. Remove from the oven and trim off the excess pastry with a sharp knife. Leave to cool.
Reduce the heat of the oven to 170C/340F/Gas 3.
For the filling, place 200g/7oz of the sugar and the water into a saucepan and heat gently until the sugar dissolves.
Add the passion fruit juice, stir well, then remove from the heat and allow to cool.
In a bowl, whisk the eggs with the remaining sugar, until pale and light, then add the cream.
Using a slotted spoon, remove three-quarters of the passion fruit pulp from the syrup and add to the cream mixture along with a tablespoon of the cooled passion fruit juice mixture. Reserve some of the remaining juices to use as extra sauce.
Pour the egg and cream mixture into the cooked tart case, then transfer to the oven on the middle shelf to bake for about 40 minutes, or until the filling has almost set. It should still be a little bit wobbly, but will carry on cooking after it is removed from the oven and will set.
To serve, dust the tart with icing sugar and drizzle with a spoonful of the remaining sauce.