You'd be surprised to note that actual fungus is not included in the list of ingredients... but lots of unusual spices and peels are. Like cloves, nutmeg, cardamon, cinnamon, ginger, orange peel, and lemon peel. Even honey makes the list.
I don't make these every year... and when I do it becomes a labor of love for my father (he always gets the most cookies to eat).
I tell folks who receive a cookie, "You don't have to like it. But I will be insulted if you do not try it." The taste is very unusual and less sugary sweet than most American cookies.
So to my Lithuanian family... all those Zanewicz's and Kallock's, Merry Christmas!