Why is Plum Pudding called Plum Pudding when there are no plums in it?
In the 17th century, plums referred to raisins or other fruits.
(1) Defination of "plum" in the Oxford English Dictionary
A dried grape or raisin as used for puddings, cakes, etc. This use probably arose from the substitution of raisins for dried plums or prunes as an ingredient in plum-broth, porridge, etc., with retention of the name 'plum' for the subsituted article." The OED then goes on to list occurances of this use in literature. Samuel Johnson defined a "plum" as "raisin; grape dried in the sun."
(2) The French perspective
This famous, typically English, dessert was given the name of plum pudding in the XVIIth century but had previously been called hackin from its many ingredients, sometimes reaching two dozen or more, which were finely chopped before being folded into the dough. The dessert was often prepared on Christmas morning and, generously sprinkled with brandy flamed as it was brought to the table, always served with great ceremony
History of Plum Pudding
Plum pudding is a steamed or boiled pudding frequently served at holiday times. Plum pudding has never contained plums. The name Christmas pudding is first recorded in 1858 in a novel by Anthony Trollope.
Traditionally in England, small silver charms were baked in the plum pudding. A silver coin would bring wealth in the coming year; a tiny wishbone, good luck; a silver thimble, thrift; an anchor, safe harbor. By Victorian times, only the silver coin remained. In England these tiny charms can still be bought by families who make their own puddings. It is also traditional for every one who lives in the household to simultaneously hold onto the wooden spoon, help stir the batter for the pudding and make a wish.
Probably the easiest thing today in America is to go to your local coin store and get a silver dime. The last one I bought cost somewhere around a dollar.