Ingredients
150g plain flour, plus extra for dusting 
30g cocoa powder 
100g chilled butter, cut into 1cm cubes 
3 tbsp caster sugar 
1 egg, yolk (freeze your white in a labelled bag) 
2-3 tbsp cold milk or water 
Pinch of salt 

Equipment Needed 
1 x 23cm deep fluted loose bottomed quiche tin 

Method
To make the pastry, put the flour and cocoa powder into a large bowl and rub in the butter with your fingertips until the mixture resembles breadcrumbs, add the sugar and mix through. Mix the egg yolk with 2 tbsp of cold milk and stir through the flour with a knife, then with your hands bring the mixture together.  I do this by squeezing and some mixture in my hand then pushing against the side.  If the mixture is not picking everything up fairly easily then add another tbsp of milk, bringing it together again in a ball.  Get a sheet of cling film and put the ball on to the cling film and then flatten the ball into a disc shape and put into the fridge for 30 minutes. 

After half an hour, preheat the oven to 180c. 

Remove the pastry from the fridge and on a lightly floured surface, roll out the dough to a circle the thickness of a £1 coin.  I find as the pastry stretches with the rolling pin it can easily stick to your work surface.  To stop this, once I have rolled a few times I lightly dust the top and then wrap around my rolling pin and turn it over then dusting the bottom (now top) a little more.  Once you are sure your pastry is large enough to fill the bottom and bases of your sides, carefully roll around your rolling pin and unroll over your tin.  Now use the pastry to line your tart tin pushing the pastry into the fluted sides, leaving the excess hanging over the edge. Pastry has a nasty habit of shrinking as it cools and cooks so this way you can be more confident it won't shrink too much. 

Put the now pastry lined tin on to baking sheet and put baking paper or greaseproof paper over the pastry bottom and fill with baking beans or rice. Put into the oven and bake for 15 minutes. 

After 15 minutes remove the baking paper and baking beans and put the tart case back into the oven for 12-15 minutes.  Check after 12 minutes, you don't want it to burn but do want it to dry out and cook in the centre.  Once you are happy the tart case is cooked, take it out and with a serrated knife, very carefully trim off the overhanging pastry.