A mille-feuille pastry
The Mille-feuille ("1000-leaf"), vanilla slice, cream slice, custard slice, also referred to as the Napoleon, is really a pastry beginning in France. The name can also be written as "millefeuille" and "mille feuille".
Typically, a Mille-feuille consists of three layers of puff pastry (pte feuillete), alternating with two layers of pastry cream (crme ptissire), but may whipped cream, or jam. The very best is generally glazed with icing or fondant in alternating white-colored (icing) and brown (chocolate) strips, and combed. Alternatively the very best pastry layer might be dusted with confectioner's sugar, cacao, or pulverized nuts (e.g. roasted almonds). Today, there's also savory mille-feuille, with cheese and green spinach or any other savory fillings.
The precise origin from the mille-feuille is unknown. Franois Pierre en Varenne described it in the book Cuisinier franois in 1651. It had been later improved by Marie-Antoine Carme. Carme, writing in the finish from the 1700s, considered it of "ancient origin."