Chocolate and orange custard tart with caramel

Method

1. For the pastry, pulse the sugar and butter in a food processor until combined. Add the flour and cocoa powder and pulse to a breadcrumblike texture. Add the egg yolk and 2 tbsp cold water, then pulse to bring the dough together – you may need a little more water, but be careful not to make the dough too wet. (If you don’t have a food processor, beat the sugar and butter with a wooden spoon, then rub in the flour and cocoa with your hands. Using a wooden spoon, mix in the egg yolk and water, then knead.)
2. Once the dough is smooth, shape into a thick disc, cover with cling film and chill for 30 minutes. Heat the oven to 190°C/fan170°C/gas 5. Roll out the pastry between 2 sheets of baking paper to the thickness of a £1 coin. Remove the top sheet of paper, then gently roll up the pastry around the rolling pin.
3. Unroll the pastry over a 23cm deep fluted tin, carefully press the pastry into the sides, then pull off the paper (see tips). Pull off the overhanging pastry to patch any gaps in the tin, then trim the remaining excess pastry from the sides with a sharp knife (or roll the rolling pin over the top to cut off the excess).
4. Scrunch up the baking paper, then flatten out and use to line the pastry case (scrunching it helps it fit into the corners). Fill with baking beans rice, then chill for 15 minutes. Bake on the middle shelf for 15 minutes, remove the beans/rice, then cook for 5 more minutes until the pastry feels sandy. Remove.
5. While the pastry is baking, make the custard. Whisk the egg yolks and sugar with a balloon whisk in a bowl until combined. Gently warm the cream in a medium saucepan until just starting to steam. Slowly pour the cream over the yolks, whisking as you go, to get a smooth custard.
6. Strain the mixture through a sieve into a jug. Using a large spoon, remove any bubbles from the top of the custard, then stir in the zest.
7. When the pastry shell is cooked, return it to the oven, pull out the oven rack halfway, then pour in the custard. Gently slide the rack back into the oven and decrease the temperature to 150°C/fan130°C/ gas 2. Bake for 30 minutes or until the tart is just set with a wobble when nudged – it will firm up as it cools.
8. Leave to cool for 10 minutes, then carefully remove the tart from the tart tin and cool for at least 1 hour.
9. For the caramel, put the sugar and 30ml cold water in a pan over a medium heat. Stir until the sugar dissolves, then stop stirring. Cook the syrup, swirling the pan occasionally, until golden brown. Keep an eye on it so it doesn’t burn.
10. When it reaches a deep golden caramel colour, carefully add the cream (it may spit) and stir until combined. Put back on a low heat to melt any solidified caramel, stirring until smooth. Add the butter and salt, then stir until combined.
11. Once the tart is completely cool, top with the orange slices. Drizzle over the just-warm caramel sauce, then slice and serve.