For the pastry

Sift the flour, cocoa powder and icing sugar into the bowl of a food processor. Cube and add the butter and a pinch of sea salt, then pulse until it resembles breadcrumbs. Add the egg yolk, vanilla extract and 2 tablespoons of cold water and pulse again, until the dough comes together. Tip out onto a floured surface and bring it together with your hands. Wrap it in clingfilm and chill for 20 minutes. Preheat the oven to 200ºC/gas 6, and insert a baking tray to warm up. On a flour-dusted surface, roll out the pastry into a 25cm circle to the thickness of a pound coin. Using your rolling pin, lift the pastry and drape it over a 23cm loose-bottomed tart tin. Ease it into place, pushing the pastry right into the corners. Roll your rolling pin over the top of the tin to cut off any overhang, prick the base all over with a fork, and return to the fridge to chill for 20 minutes. Take the tin out of the fridge and line it with greaseproof paper, then fill with baking beans or rice. Bake it in the oven for 15 minutes, then remove the paper and beans and return it to the oven for 5 minutes, until dried. Set aside to cool.

For the filling

Put the cream, tea and caster sugar in a pan, place it over a medium heat and bring it to the boil. Break the chocolate into a bowl, pour over the hot cream mixture and stir until all the chocolate has melted. Beat the eggs, then stir them into the mixture. Return to the oven for 20 minutes, or until the filling is almost set but still has a little wobble in the centre. Leave on a cooling rack to cool completely, then ease the tart out of its tin, slice and serve.