Rick,
The cookie you are looking for is called "Lebkuchen". There are many, many
recipes for it; basically, it is a spice flavored cookie. I have an old
family recipe (been in may family at least since my great-grandmother) that
is a bit unusual -- it is not a cookie per say, but more like a very thick,
chewy brownie (in texture only -- there is no chocolate). Since the only
fat is from the eggs, it tends to go stale quickly (and thus your
description of "hard as a rock" struck home!), but this is usually remedied
by putting the lebkuchen in a bowl or tin wrapped in a kitchen towel soaked
in brandy.
The ingredients for most lebkuchen include flour, eggs, brown sugar,
cinnamon, cloves and nutmeg. If you would like my family's recipe, let me
know, and I will send it to you. But if what you remember is truly a
cookie, not a bar, then you should have no trouble finding a recipe in any
international or Christmas cookie book.
Good luck! Barbara