Sieve the flour and cacao powder with a pinch of salt. Whisk the butter and sugar in a bowl. Mix this with the egg and chocolate.
Add the flour mixture and knead this into a dough. Add a little extra flour if needed for a better (less sticky) dough. Shape into a round disk and cover with plastic wrap.
Leave to rest for 30 minutes in the fridge.
Roll out the dough and put into your baking tin (round 25 cm. low edge) and put the tin back into the fridge for about 15 mins.
Preheat your oven in the meantime to 200˚ C. Take the tin out of the fridge and cover the dough with a piece of baking paper. Weigh this down with baking beans.
Blind bake your pastry for about 15 mins. Then take out and remove the baking paper and beans and bake for another 5 minutes. Leave to cool.
Decrease the temperature of your oven to 170˚ C.
Brush about 1/3 of the melted chocolate over the bottom of the crust. Bring the milk and cream close to the boil and pour this over the chocolate pieces. Let it stand for a bit and mix until it becomes a smooth chocolate cream. Leave to cool to room temperature.
Whisk the eggs, sugar and vanilla in another bowl and mix this together with your chocolate cream. Pour the mixture into the tin and bake for 40-45 minutes at 170˚ C.
Let it cool down completely before handling and removing the tin. Once done, dust with a sprinkling of cacao powder (optional)