Flies' graveyard, or "flies' cemetery" are nicknames used in various parts of the United Kingdom for sweet pastries filled with currants or raisins, which are jokingly said to resemble dead flies. In Scotland, they are known as "fly cakes", "fruit slice" or "fruit squares" and in Northern Ireland as "currant squares". In the North East of England, the pastries are "fly cakes" or "fly pie", and in Wales it is called "Cacen Pwdin" ("dessert cake").

It gets its name from the fact that the dense, black mush on the fruit resembles a homemade flytrap at the height of summer. There is a mention of these cookies in the 1855 "Glossary of Yorkshire Words".

It has a layer of raisins or currants sandwiched between two layers of cookies or cakes. They can be frosted, creating what look like simple white tombstones, or simply sprinkled with powdered sugar.

There are variations on how this fruit slice is made: some people use puff pastry instead of shortcrust pastry. Note that the word 'raisin' is generally reserved for the large dry dark-colored grape, and 'currant' is a small dry black currant.

The most common suggest using plain pastry dough, a combination of butter, shortening, or margarine, flour, salt, and a little water. Other recipes suggest adding sugar or egg to the dough. Some recipes suggest adding a bit of the currant or raisin mixture to the dough, so you can see a few "dead flies" on the top and bottom of the cookie.

More Info: en.wikipedia.org