Amazing, if you want to try, check out Eastern European shops near you. They sometimes stock these. My local does, though i haven’t tried shop bought ones yet.
One if my earliest childhood memories was when i was maybe 5 or so, and you would make them with your neighbours for a new year party celebration. Amazing home cooked for sure 
I didn’t, i was about 5 at the time, but still remember that experience 
Normally back then you would take condensed milk (i prefer unsweetened) can and boil it for about 3 hours to make the filling. Its very close to Dulce de Leche. Back then we didn’t have premade stuff being sold. Be careful though i only done it a handful of times (boiling it) so make sure no part of the can is ever exposed to the air and always have water covering it.