I am looking at the Old Fashioned Tomato Salad recipe and wondering why it starts "Half fill a sink with cold water"?
The salad cream is a cooked dressing made with milk and vinegar and thickened with flour and egg, rather like a savoury custard (crème anglais). The base of the saucepan is dipped into the sink of cold water as soon as the sauce has thickened. This stops the cooking immediately and reduces the risk that the egg starts to scramble, which would make sauce grainy. Dipping the base in cold water also helps to cool the dressing quickly. The salad cream can be stored in the fridge in an airtight container for up to 3 days.