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.