Q. I have a Danish cookbook with recipes for Christmas cookies. Several of them call for hartshorn, also called bakers ammonia. I cannot find it. I have tried pharmacies, bakeries, and old-time bakers. Is there a substitute I can use or a source you know of?
A. Hartshorn is a leavening agent, and a precursor to the baking soda and baking powder that everyone uses these days. Hartshorn’s virtue is that it readily breaks down into a gas when heated (causing the leavening), but unless it escapes completely, it leaves a hint or more of the smell of ammonia. For that reason, it is generally used only in cookie recipes where it doesn’t have to fight its way out of a deep batter.
Another name for hartshorn is ammonium bicarbonate, and it should be available in at least some drug stores, but you must first grind it to powder to use it. The Baker’s Catalog at King Arthur Flour doesn’t carry it, so as far as we’re concerned, it is not an essential aid to baking. We think substituting baking powder (at a ratio of 1 teaspoon per cup of flour) would be a perfectly good solution to your problem. If the recipe you’re using includes a particularly acidic ingredient (such as buttermilk), you might instead substitute baking soda for the hartshorn, in the ratio of 1/4 teaspoon per cup of flour.