Heat the milk with the cinnamon stick to just under boiling point. Lightly beat the eggs with the sugar, and then add the corn flour and flour. Pour the hot milk into this mixture, stirring rapidly. Return the mixture to the heat and cook, stirring until the mixture becomes thick. Keep stirring while it is cooking to prevent it from catching on the bottom of the pot and getting lumpy. Take the mixture off the heat and add the vanilla essence and butter. Stir well until the butter is melted. Pour the mixture into the prepared tart crust. Sprinkle with cinnamon sugar.