Could I put a hot milk cup in a cold water bowl to let it cool down?

Yes! The cornstarch thickens the sauce by undergoing a process called gelatinisation that requires a temperature of at least 60 degrees Celsius/150 degrees Fahrenheit.

Put cold water in your coffee maker. The coffee maker will heat up the water automatically.

For some this is a preference, for others it is not. Calling a preference "correct" or not is taking it too far -- ask people before making an assumption about...

It will cool slower, as the metal in the cup will conduct the heat and keep it warmer longer.

It’s your choice whether you want to put anything in there or not, but usually it’s left clean/empty.

Although she clearly did nothing to earn your business, she did not seem to violate any laws or regulations. If you want to warn others of her antics, you best...

Yes, of course. It has the same ratio, which is all that matters. You can double, half, triple, etc. any recipe, and will just end up with more or less...

Hot water.

I would use warm water, it would likely increase the oil output of the rose.

Air in the pipes makes them bang.