If you don’t know what a sugar plum is, you’re in good company. The Oxford English Dictionary declares the term obsolete, and so it is. “Sugar plum” was well known to English-speakers from the 17th to the 19th century as another name for what was sometimes called dragee or more commonly comfit. I suspect that doesn’t really clarify matters. All of these terms name a sweet made of sugar hardened around a central seed or kernel in successive layers using a process called “panning.” The glossy sugar shells on candies like jelly beans or M&Ms are produced through a similar process: The candy pan is kept in motion over heat, while successive layers of sugar are poured on and allowed to harden. Jawbreakers are made this way, using a sugar crystal as the seed. Sugar plums or comfits were most often made with caraway or cardamom seeds at the center. Almonds were another classic base for sugar plum; the resulting candy would be like what we call Jordan almonds.
Confectionery historian Laura Mason calls comfit-making “one of the most difficult and tedious methods in craft confectionery, requiring specialized equipment, careful heat control, and experience.” Depending on the size of the finished product, a batch could take several days to complete. Not just anybody could make these candies. Until the advent of machine innovations, comfits or sugar plums were a luxury good, most likely to be found in an aristocrat’s pocket or between courses at a banquet.