A leavening agent, and the forerunner of today's baking powder and baking soda. Originally made from the ground antlers of reindeer, this is an ancestor of modern baking powder. Northern Europeans still use it because it makes their springerle and gingerbread cookies very light and crisp. Unfortunately, it can impart an unpleasant ammonia flavor, so it's best used in cookies and pastries that are small enough to allow the ammonia odor to dissipate while baking. Can be found in German or Scandinavian markets, drug stores, baking supply stores or a mail order catalog. Must be ground into a powder before using. Don't confuse this with ordinary household ammonia, which is poisonous.
1 teaspoon of baker’s 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