An éclair is an oblong pastry made with choux dough filled with a cream and topped with icing. The dough, which is the same as that used for profiterole, is typically piped into an oblong shape with a pastry bag and baked until it is crisp and hollow inside. Once cool, the pastry is then filled with a vanilla-, coffee- or chocolate-flavoured custard (crème pâtissière), or with whipped cream, or chiboust cream; and then iced with fondant icing. Other fillings include pistachio- and rum-flavoured custard, fruit-flavoured fillings, or chestnut purée. The icing is sometimes caramel, in which case the dessert may be called a bâton de Jacob.
In 18th and 19th century France, gas ovens did not exist. Huge brick ovens were used, which took a long time to heat up but also to cool down. Bakers used the ovens during the cooling process, taking advantage of their stored heat, for baking pastry. This was called baking à petit four (literally "at small oven"), a lower temperature which allowed pastry baking.
This bread tastes like a warm-from-the-oven cinnamon bun — without the fuss of rolling and cutting.