Line the bottoms and sides of 2 pie plates with the puff pastry and make a raised edge for each. To make the filling, add the butter, salt and cinnamon to the boiling milk. Mix the custard powder ,cornflour and cake flour to a paste with the cold milk. Stir in a little of the milk mixture. Stir the custard mixture into the hot milk, add 50 ml of the Sugar and bring to the boil, stirring continuously. Remove from the stove when it has thickened and discard the cinnamon. Beat the egg whites until stiff but not dry. Gradually beat in the remaining Sugar. Beat the egg yolks lightly and stir in a little of the custard mixture. Stir the yolks into the custard mixture, then add the almond extract. Carefully fold in the egg whites. Pour the mixture into the pastry cases and bake at 200 C for approximately 10 minutes. Lower the temperature to 180 C and bake for a further 10–15 minutes, or until the filling has set. Cool slightly and sprinkle the tart with cinnamon sugar.