Lemon drops are made by boiling sugar, water and cream of tartar until it reaches the hard crack stage.

As the mixture cools, lemon flavor is added.

Lemon drops originated in England, where confectioners learned that adding acid such as lemon juice to the boiled sugar mixture prevented sugar from crystallizing.

[1] The term "lemon drop" is also occasionally applied to lemon-flavored throat lozenges, and is the namesake of a cocktail consisting of lemon juice, vodka and sugar.

Modern lemon drops, like most hard candies we know today, descend from ancient medicinal lozenges.