Take a large bowl with ice water and cubes before making a well in the center for the custard. Place it so the base is submerged, stirring and rotating occasionally.
This way, you can cool your custard quickly and prevent any unsightly skin from forming on a hot custard as it cools. It will also keep the custard smooth and lump-free.
Additionally, cooling a curdled custard in an ice bath and whisking it can bring it back from the brink, keeping it from developing an unappetizing texture and lumpy consistency.