Religieuse

A religieuse is a French pastry made of a small choux pastry case stacked on top of a larger one, both filled with crème pâtissière, commonly flavoured with chocolate or mocha. Each case is topped with a ganache of the same flavour as the filling, then attached to each other using piped buttercream icing. It is a type of éclair. The pastry, whose name means "nun", is supposed to represent the papal mitre. The religieuse was supposedly conceived in the mid-nineteenth century; choux pastry was invented in the 16th century.

Source: Wikipedia