Mix together the cornflour and 250ml water to form a smooth paste (whisk vigourously to make the batter smooth).
Mix the 1.5 lt water with the sugar in a large pot until the sugar dissolves then add the cardamom powder and gradually stir-in the cornflour mixture and the ghee. Mix thoroughly until everything combines.
Heat on medium heat, stirring continuously with a wooden spoon for the first 20 minutes. After that go back every 10 minutes or so to stir.
Keep cooking for about 3 hours, until the mixture thickens and the ghee separates out. Pour the ghee from the pan, put the xalwa (also known as halwa) in a separate pan and decorate with peanuts and sesame seeds.
When cooled slice with a wet knife. Wrap in cellophane or waxed paper.