hi I had never heard of it before, so I looked it up Here is a site that explains what it is: http://www.foodsubs.com/Leaven.html#baker's%20ammonia
(did you read the part abt reindeer antlers??)
Substitutes (for 1 teaspoon of bakers ammonia): 1 teaspoon baking powder (This is very similar, but might not yield as light and crisp a product.) OR 1 teaspoon baking powder plus 1 teaspoon baking soda