Ganache is a mixture of chocolate and cream, and its origins have been debated by culinary historians. They agree that it was invented around 1850, but some contend that the Swiss developed it while others argue that it was created at the Parisian Patisserie Siravdin (References 1). Beyond these brief facts, further knowledge is difficult to find about its specific history.
The basic ingredients are melted chocolate (dark or milk) and double cream. One can add butter or sugar as well. Other additions can be made, such as extracts (i.e. vanilla or almond) or liqueurs. A chef may alter the density of the ganache by tinkering with the ratio of chocolate to cream (References 2). Ganache has a variety of uses, and depending on the temperature and density of the ganache, it can achieve multiple forms.
Uses for Ganache - Warm
Warm ganache can be drizzled over a cake to create a glaze. It can also serve as a filling in a warm cake, such as a molten lava cake.
Uses of Ganache - Cold
Cold, dense ganache can be moulded into truffles. Creamy and cold ganache can be whipped into a frosting or a filling.