A rare instance of the singular occurred in the respected
toilet-humour magazine
Viz. Writing about a
waif-thin teenage
supermodel who was denying that she had
anorexia, she made the obligatory disclaimer that she had a hearty
appetite, and "tucked into a hundred and thousand".
Strictly, hundreds and thousands are spherical, and the cylindrical ones are called sprinkles or dollars, but obviously the noders above and below me reflect a common usage.
Hundreds and thousands sandwiches are the only known use of white bread. It must be white with its horrible plastic chemical taste to bring out the sweet texture properly. Usually it is buttered to enable them to adhere, but I have to recommend, if only as a test of perversity, the unbuttered inch-thick hundreds and thousands sandwich, sealed at the edges with finger pressure only.
Then I grew up.