For the pastry
175g plain flour, plus a little extra for dusting
80g icing sugar
40g 70% cocoa powder, the best quality you can find
140g butter, chilled and cut into small cubes
2 medium egg yolks, lightly beaten
For the filling
185ml whole milk
185ml double cream
60g white caster sugar
4 egg yolks
300g white chocolate
For the syrup
6 passion fruit
75ml caster sugar
100ml orange juice
To make the pastry, sift the flour, icing sugar and cocoa powder into a small food processor. Add the butter and blitz together until it is the texture of breadcrumbs. Add the egg yolks and mix together gently with your fingers until it forms a soft paste. You may need to add a little water, 1 tbsp at a time. Wrap in cling film and place in the fridge to rest for at least 1 hr.
Heat oven to 190C/170C fan/ gas 5. Roll out the pastry on a lightly floured surface to the thickness of a pound coin. Use the pastry to line a 20cm round tart tin with a slight overhang. Prick the pastry with a fork and chill in the fridge for 1 hr. Line the inside of the pastry case with baking parchment and fill with baking beans, uncooked rice or dried pulses to keep the base flat. Place the tart tin on a baking sheet and bake for 25 mins. Remove from the oven, take out the parchment and beans and return to the oven to cook for a further 10-20 mins until the pastry case is cooked through and dried out. Remove from the oven and leave to cool. Trim off the excess pastry with a serrated knife.
To make the custard filling, pour the milk, cream and sugar into a saucepan and bring to the boil. Remove from the heat and put the egg yolks in a bowl. While whisking the yolks, pour in the cream mix, until fully incorporated. Pour the custard back into the saucepan and heat to 85C (use a digital probe to check the temperature), or until it’s thick enough to coat the back of a spoon. Tip the white chocolate into a large bowl and pour over the hot custard, stirring to make a rich chocolate custard. Leave to cool, then ladle the custard evenly into the pastry case and chill for at least 2 hrs, or overnight if possible.
For the passion fruit syrup, cut the fruit in half, scrape out the seeded flesh into a saucepan and add the caster sugar and orange juice. Put the pan on a medium heat, bring to the boil and simmer for 25 mins until thickened and syrupy. Remove from the heat and leave to cool. Can be made several days ahead. Pour the chilled passion fruit syrup over the chilled tart just before slicing.