The mille-feuille (French pronunciation: ​[mil fœj], "a thousand leaves"), vanilla slice, custard slice, also known as the Napoleon, is a French pastry whose exact origin is unknown. Its modern form was influenced by improvements of Marie-Antoine Carême.Traditionally, a mille-feuille is made up of three layers of puff pastry (pâte feuilletée), alternating with two layers of pastry cream (crème pâtissière), but sometimes whipped cream or jam are substituted.