Check the consistency by lifting a spoonful of custard, tilting it, and drawing a line across the spoon with your finger. It is ready when the two edges separate neatly.
Pour the custard through a sieve and into a clean bowl. Place this in a larger bowl containing crushed ice. Chill rapidly over the ice, stirring and scraping the sides of the bowl continuously. Refrigerate for up to 24 hours.
