Tenderly spiced with cardamom puffy shells, Choux pastry or pate a choux is an unusual pastry in that flour is added to a boiled mixture of butter and water (roux like) and then cooked until it forms a smooth ball of dough. After cooling the dough to lukewarm, eggs are slowly added and the dough is beaten until it becomes a smooth thick paste. The the dough can either be piped or dropped into mounds onto a baking sheet and then baked, first at a high temperature and then at a slightly lower temperature. The high temperature is needed so the dough will rise quickly (giving it a hollow center) and to set the structure of the shells. Bakers' Ammonia is a leavening ingredient called for in many old world recipes, especially those from Scandinavia. It is also called hartshorn . Unlike baking powder or soda, Bakers' Ammonia (ammonium carbonate) leaves no unpleasant alkaline off-flavor in baked goods. You can find it in any major supermarket or a Greek store.