French for a 'thousand leaves', a dessert made with two (can have more layers or different shapes) oblong pieces of crisp puff pastry

spread with whipped cream, custard, jam or fruit puree.

The layers of puff pastry  are stacked and topped with another pastry layer. The top is sometimes finished with a glaze and a chocolate design or dusted with icing sugar.
                                                             Talking about Mille-feuille : Three by three...