This is a Trianon, also called chocolate royalTrianon, aussi appelé "royal au chocolat"
 
It is a classic French dessert made with a crispy hazelnut meringue – dacquoise – and crunchy praline feuillantine (French pronunciation: ​[paj.te fœj.tin]). Then it is topped with a thick layer of rich dark chocolate mousse. Finally, it is covered with a cocoa mirror glaze and decorations
 
biscuit dacquoise noisette, Croustillant praliné feuillantine chocolat, Mousse au chocolat à base de crème anglaise, Glaçage miroir au cacao