Close. You're mixing up your harts and hounds, and horns and whorxxx..., um, well never mind.

Your mother made Christmas cookies using hartshorn, or ammonium bicarbonate, as the leavening agent. If you read the hartshorn article, you'll find our suggestions for dealing with it in recipes.

Horehound is a plant (marribium vulgare), a member of the mint family, native to Europe and Asia but successfully transplanted to North America. Its leaves are used in making a tea and also a hard candy, characterized by a slightly bitter taste. Some people believe that horehound was one of the original bitter herbs of the Jewish Passover.

It is quite possible that your mother made candy with horehound while she was making cookies with hartshorn, which could certainly have led to confusion in your childhood memories. ("Why, for heaven's sake, is mama making bitter candy, when we have all these ammonia-smelling cookies to eat up?" you might naturally have asked.)

Horehound is widely available online as a cure-all for just about everything.