Sieve the flour, cocoa and icing together and a punch of salt together in a bowl, using fingertips break butter into small chunks rub into flour mix , using a knife mix in the egg yolk and 2 teaspoons of cold water to bring the mixture together into a smooth dough warp in cling film and chill for 30 minute. Preheat oven to gas mark .
Roll out pastry onto on a lightly dusted surface and use to line a 20cm tart tin, 4cm deep. Line the pastry with non-stick baking paper and ceramic baking of dried beans and bake for 20 minutes. Remove baking paper and bean and return to oven for 5 mins until pastry is cooked. Leave to cool. Turn the oven down to gas mark 4.
Whisk the milk egg yolks both flours and crème fraiche in a pan until smooth. Bring to the boil add half the blueberries and cook stirring constantly and squashing the blueberries until the custard turns a deep purple. Add the other half of blueberries and stir again until hot. Place the baking pastry case directly onto a baking tray and spoon in the hot blueberry custard.
For the meringue, whisk the egg whites into a thick frith and gradually add the sugar until very thick and glossy. Sieve over corn flour then fold it into the meringue mixture. Spoon mixture over custard and spread into peaks. Lightly dust with cocoa and bake in over for 15- 20 mins or until just set, leave until cod and then serve.