Roll the pastry out thinly on a lightly floured surface and use to line a loose-bottomed 23cm round, 5cm deep fluted flan tin. Press the pastry into the sides and patch any gaps. Stand the tin on a baking sheet. Line the pastry case with baking parchment and baking beans and rest in the fridge for 20 minutes.
Meanwhile, heat the oven to 400°F/200°C/gas mark 6. For the filling, pour the milk into a pan and add the cardamom and cinnamon. Bring just to boiling point, then remove from the heat and leave to stand for 15 minutes to allow the flavours to infuse.
Bake the pastry case ‘blind’ for about 15 minutes, until the pastry is just set. Remove the paper and beans, then return to the oven for 5 minutes to cook the base. Turn the oven down to 180°C/gas mark 4.
In a large bowl, mix together the sugar, cornflour and egg yolks. Strain the milk through a fine sieve into a jug, then gradually stir into the egg mixture. Whisk the egg whites until softly stiff and fold into the egg yolk mixture.
Pour the filling into the pastry case. Bake for 20 minutes or until the filling is brown on top, then turn the oven down to 225°F/110°C/gas mark ½ and bake for a further 1 hour until the custard has just set. It should have a slight wobble in the centre.
Leave to cool completely before serving.