Many of my more advanced recipes such as custards and curds will call for an ice water bath to be set up before the start of your recipe preparations.
An ice water bath is necessary for when you must cool down liquids quickly.
In the case of custards, even after you take it off the heat, carryover cooking can cause the temperature to continue to rise.
The ice bath will immediately stop the cooking process , since that residual heat that can so quickly turn your perfect custard into a bowl of scrambled eggs.
To make your ice water bath, place a good amount of ice and a moderate amount of water in a very large bowl, then nestle a smaller metal bowl into the ice water.
You will then pour whatever recipe you are cooling, (usually through a strainer) and into the smaller bowl. Quick cooling will ensure there will be no curdling AND more importantly NO DANGER of bacteria forming as it could if you let that custard cool at its own leisurely pace!
Note: It is best to use a metal bowl. Since metal is a good conductor, it will actually conduct the heat of the custard into the surrounding ice.