.My Polish friend told me it was Hungary cake
was it a dessert? we eat placek węgierski (hungarian pancake) but it's not sweet. it's a kind of pancake made of grated potatoes and served with sauce (with beaf, I think). that's the only dish I know that has "hungarian" in its name.
a crusty bread bun which was hollowed out and had soup in it
It must have been ŻUREK, that's the only soup we serve in a bread bun. but not every restaurant serves it like that, żurek is also served in a plate:)so you should say you want
żurek w chlebie (zurek in a bread bun)