Despite the pleasant feeling of hot drinks during the cold winter weather, sometimes hot is too hot. When you can't cool off a hot cup of coffee or cocoa in the fridge (or by putting it outside), you can reduce its temperature pretty quickly with a saucer.
Photo by Joelk75
StackExchange user Bob Murphy explains how you can easily cool a hot cup of anything with a little trick called "saucering":
If you want [a fast]way to cool a cup of coffee...pour the top part of it from the cup into a saucer, and then back again a few times. The large and constantly changing surface area during this process will cause extremely rapid evaporation of those high-energy outliers, much faster than stirring. Saucering was very common up through the Great Depression, which is one of the reasons older coffee sets always included saucers. You also get deep-ish saucers at many restaurants as a holdover from this practice, although I doubt many people do it anymore.
Next time you're in a coffee shop and need to cool off that cup quickly, you might get the job down quicker if you ask for a saucer.
Cooling a cup of coffee with help of a spoon [StackExchange]