White and dark chocolate and cardamom tart

Method

1. For the pastry, cream the butter and sugar with an electric whisk until pale and fluffy. Add the egg yolks one at a time, whisking well between additions. Sift the flour into a bowl and mix with the cocoa.
2. Add a little bit of the flour mix to the creamed butter mixture, then a little bit of the water. Mix until incorporated. Keep doing this until all the flour and water are mixed in and the mixture has formed a smooth dough. Knead briefly, then shape into a disc, wrap in cling film and chill for at least 1 hour.
3. Preheat the oven to 180°C/fan160°C/gas 4. Roll out the dough between two pieces of baking paper to a 28cm circle, about 5mm thick. Peel off the top layer of baking paper, turn over and drape the rolled dough into a 21cm x 3.5cm deep loose-bottomed tart tin (paper-side up). It will sag under its own weight. Push it down carefully to line the tin. Don’t peel away the paper and don’t worry, at this stage, about trimming the pastry. Fill with baking beans or rice and put on a baking sheet. Blind-bake for 15 minutes, then take out of the oven and remove the beans/rice and baking paper. Return to the oven for 10 minutes to crisp up the base. Remove and leave to cool.
4. For the filling, crush the cardamom pods in a pestle and mortar, remove the green husks and grind the seeds to a fine powder. Heat the crème fraîche with 125ml of the double cream in a pan until almost boiling, remove from the heat, then add the ground cardamom. Whisk the two egg yolks in a bowl, then slowly pour over the hot cream while whisking continuously. Add the white chocolate and whisk until melted.
5. Whisk the remaining cream until it forms soft peaks, then fold it into the cream and chocolate mixture. Pour into the prepared pastry case, then cook for 15 minutes. Remove from the oven, cool, then chill for at least 2 hours to set before serving.