Put the chocolate in a heatproof bowl. Heat the cream in a saucepan until it just boils, then pour it over the chocolate. Stir until smooth, then beat in the egg yolks. Tip the mixture into a jug, then pour into four individual pots and put in the fridge to set for at least 2 hrs.
Meanwhile, put the flour, orange zest and butter in a large bowl and rub together until it resembles fine breadcrumbs. Add the sugar and egg yolk, mix gently and bring the biscuit dough together with your hands. Roll the shortbread out on a lightly floured surface until 1cm thick, then transfer to a baking tray lined with baking parchment. Leave to rest for 10 mins in the fridge.
Heat oven to 160C/140C fan/ gas 3. Bake for 23-25 mins until golden brown, then sprinkle with sugar. While still warm, cut into eight x 2cm biscuits, trimming off any excess, and leave to cool.
When ready to eat, whip the cream to soft peaks, then spoon on top of the chocolate pots. Serve with the shortbreads on the side.