During my wanderings around Varna, I also came across the so-called soldier’s cookies (Войнишка курабия). It is an old biscuit recipe that is currently gaining popularity again.
The basis of the dough is eggs, sugar, yogurt, flour, and baking soda. The dough is already very thick before baking, the whole recipe including the procedure is shown in this video:
Just like with kurabiiki cookies, this biscuit is also dense and crispy. I can imagine that it lasts a very long time. This Bulgarian sweet bought directly from the bakery costs approximately 0.24 EUR.