The story goes that during the Napoleonic blockades, getting cocoa to Europe from South America was almost impossible. To extend what cocoa was available, people began to add hazelnuts, a technique perfected in mid 19th-century Piedmont, using a paste of toasted hazelnuts. It was named gianduja after Gianduja, the archetypical 18th-century Piedmontese figure carnival mask.
It's a popular gelato flavour and is also used to make Gianduiotti as well as Nutella.
Images by: cuisine de thomas