Hitlerszalonna or Hitler-szalonna (Hungarian "Hitler bacon") was a dense fruit jam, although there is debate about how much fruit was actually in it and how edible it was, that was eaten by Hungarian troops and civilians during World War II. It was made from mixed fruits such as plum and sold in brick shaped blocks held in a piece of paper rather than in a jar. These slabs were sliced, a bit like szalonna (bacon). Soldiers kept it in a case and it could be cooked with other foods. The term itself is considered slang and defined as something like "tough fruit".
One possible source of this name derives from food provisions given to Hungarian soldiers. In armed conflicts during the Austro-Hungarian Monarchy, Hungarian soldiers received normal bacon as their food supply, which was referred to as "Kaiser-bacon". (Compare Kaiser roll.)
During World War II, Hungarian soldiers received food provisions from the Germans, and it was often fruit flavored jam instead of bacon. So the soldiers started to refer to this jam as the emperor's bacon, and the "emperor" was Adolf Hitler.
This expression has also appeared in a printed book. When describing the Hungarian army's logistical situation at the Don River near Stalingrad, and before the Battle of Stalingrad, the account (as translated below into English) states that:
The food supply of the Hungarian soldiers was not adequate ... Not only the Hungarian armies suffered from the lack of proper food but also German troops; but for the Hungarian soldiers there was an additional drawback, that the food was German, and these German foods (like pudding, anchovy paste, cheese in a tube) were uncommon and not popular among the Hungarians. Only one German food has been accepted by the soldiers and was even brought back to Hungary and became a normal product in those days and that was the "Hitler bacon" which is a flavoured jam made from pumpkin.