Christmas pudding is a pudding traditionally served on Christmas

Christmas

Christmas or Christmas Day is an annual holiday generally celebrated on December 25 by billions of people around the world. It is a Christian feast that commemorates the birth of Jesus Christ, liturgically closing the Advent season and initiating the season of Christmastide, which lasts twelve days...

 Day (December 25). It has its origins in medieval England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

, and is sometimes known as plum pudding or plum duff, though this can also refer to other kinds of boiled pudding involving dried fruit.
Many households have their own recipe for Christmas pudding, some handed down through families for generations. Essentially the recipe brings together what traditionally were expensive or luxurious ingredients - notably the sweet spices that are so important in developing its distinctive rich aroma, and usually made with suet

Suet

Suet is raw beef or mutton fat, especially the hard fat found around the loins and kidneys.Suet has a melting point of between 45° and 50°C and congelation between 37° and 40°C....

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