Using some spare butter, grease your fluted tart tin, using your pastry brush to get into all of the grooves.
Place your flour and sifted icing (confectioner's) sugar into your food processor with the blade attachment fitted, or into a large bowl if making my hand, and whizz a little to mix together
Grate or cut your butter up into small chunks and dot over the flour mixture (your butter needs to be really cold for this, if it warms up as you grate it pop it back into your fridge to reset).
Pulse again, about 15-20 times or until it turns into a san-like consistency and no large lumps of butter remain.
Add your cold egg yolk, cold orange juice and vanilla extract and pulse again until the mixture starts to form large clumps.
Tip out onto a lightly floured work surface and bring together into a ball, but do not knead.
Roll out to a circle of 30cm, drape over your rolling pin and then transfer to your tin, draping it over the top.
Push the pastry into the bottom of the tin first, then work your way up the fluted edges ensuring the pastry is pushed into the groves. Your pastry needs to rise about a centimetre above the edge of the tin rim, this allows it scope to shrink a little when baked.
Prick the base of the pastry with a fork, ensuring you press right through to the base of the tin and then refrigerate for at least 30 minutes.
Meantime heat your oven to 170°C Fan/190°C/375°F/Gas mark 5 and place a baking sheet onto the middle shelf to heat.
After 30 minutes take a piece of foil and use it to cover the base and sides of the pastry, then fill with a layer of baking beans (or rice).
Place on the baking tray in your oven and bake for 20 minutes, then remove and baking beans and foil (be careful the baking beans will be very hot) and return to the oven for another 5-10minutes. When done, the pastry case should be ¾ baked, remove from the oven and leave to cool whilst you make your chocolate filling.