Mix coconut milk, salt and sugar in a pan.
Place it over medium heat and allow it to become hot till you see bubbles on the sides of the pan.
In the meantime make the slurry by mixing cornflour or arrowroot flour with the water.
When the coconut mixture becomes hot, stir it continously and slowly pour in the slurry.
Keep stirring till the mixture becomes thick and starts leaving the sides of the pan.
Pour the mixture into a tray. Use either a 5"X 5" or a 6"X 6" tray.
Bang the tray gently on the worktop to level out the mixture. Can even use a spatula to make the top smooth.
When the mixture cools down a bit put the tray in the fridge to allow Haupia to set for about 2 hours.
Cut the set Haupia into squares and serve.