Wikipedia
Napoleonka (kremówka) (, german Cremeschnitte) is a Polish type of cream pie. It is made of two layers of puff pastry, filled with whipped cream, creamy buttercream, vanilla pastry cream (custard cream) or sometimes egg white cream, and is usually sprinkled with powdered sugar. It also can be decorated with cream or covered with a layer of icing.
In some places in Poland the cake is known as kremówka (roughly translated as "cream cake"), in others, it is called napoleonka. This Polish "war" between names kremówka and napoleonka has been subject to a satirical drawing by Polish illustrator Andrzej Mleczko.
The cake itself is a variation of mille-feuille - a French dessert made of three layers of puff pastry filled with cream or jam - also known as the Napoleon.
Sometimes kremówkas containing alcohol are sold, those became popular particularly in the aftermath of a false story that Pope John Paul II was fond of that variant. In fact, the Pope was fond of the traditional kremówka.