Preheat the oven to 180°C/350°F/Gas 4.
Place the cocoa powder, flour, caster sugar into a bowl.
Rub the butter into the mix until it resembles breadcrumbs.
Add the beaten egg and bring together with a fork.
Roll out into a round large enough to fit a 25cm fluted tin.
Press the pastry into the tin and chill in the fridge for 10 minutes.
Line the pastry with greaseproof paper and fill with baking beans. Bake for 15 minutes, remove from the oven and lift out the paper and baking beans.
Bake the pastrty case for a further 5 minutes.
Remove from the oven, cool for 10 minutes, then trim off the excess pastry.
Turn down the oven to 140°C/275°C/Gas 1.
To make the filling place the chocolate into a large bowl.
Bring the milk and cream to the boil in a pan, then pour ovr the chocolate, whisking until the chocolate is melted.
Add the beaten eggs and whisk until smooth.
Pour the filling into the pastry case and cook for 25 minutes until just set.
Allow the tart to cool before removing the tin.
Top with chocolate curls and serve.