Preheat the oven to 180°C.
In a large pot, dilute the condensed milk with the water and make sure all the condensed milk has been dissolved.
Heat the mixture until it steams, stirring continuously. Don't let a come to the boil.
Mix the dry ingredients with a little cold milk or water to form a paste. Mix until there are no lumps.
Once the milk mixture is steaming, remove from the heat and temper the flour mixture by adding a ladle or two of the hot milk mixture to the paste and mix.
Now add the flour and milk mixture into the hot milk and stir well.
Return to medium heat and stir continuously until the mixture thickens.
Stir in the egg yolks and remove from the heat.
Add the butter and vanilla essence to the thickened milk mixture and stir - leave to cool.
Beat the egg whites until light and fluffy.
Fold the egg whites into the mixture carefully.
Pour the mixture into the 3 unbaked pie crusts and bake for 15 to 20 minutes until the filling is set.
Remove from the oven and sprinkle lightly with ground cinnamon. Serve hot or cold.