Mix the flour, sugar and salt in a bowl. Cut the cold butter into pieces, add to the bowl, rub together using your hands to form an even, crumbly mixture.
Beat the eggs, add and mix quickly to form a soft dough – do not knead. Flatten the dough, cover and chill for approx. 30 mins.
Grate the lemon zest, combine with milk and vanilla in a pan, bring to the boil.
Beat together the eggs and sugar in a bowl, add the cornflour and flour and stir until smooth.
Add approx. 200 ml of hot milk to the eggs, stirring constantly, stir until smooth. Add the egg mixture to the rest of the milk in the pan. Simmer over a low heat for approx. 12 mins., stirring constantly.
Immediately press the crème through a sieve into a bowl, cover with cling film and leave to cool completely.
Halve the dough, roll out to approx. 3 mm thick on a lightly floured surface. Place one half in the prepared tin, pressing down firmly around the edges. Spread the crème over the pastry base.
Place second pastry half on top of the crème and press the edges down firmly.
Prick the lid all over with a fork. Beat the egg white and spread over the dough, scatter over the pine nuts. Bake for approx. 60 mins. in the lower half of an oven preheated to 160°C. Remove the tart and allow to cool completely in the tin before dusting with icing sugar.