The bun is some kind of bread.
From real bread... possibly sourdough to rye or something else...to this baked sponge that is popular.
Sponge is not that thing used to clean with...it's a baking thing. Where flour, water, and yeast are already mixed and the yeast is activated and growing. The full amount of flour is added to this sponge and bread is made from it.
But...to make the bread super soft...they just bake the sponge. And that's what covers the grocery store shelves today.
What I found unique was the brown bread of Europe. The wheat was locally grown and ground into flour. It wasn't bleached but wasn't exactly "whole wheat" either.
But the bread was fresh and great. Baked daily and delivered. It wasn't white...but wasn't rye or barley either. Good stuff. I'd have loved to take a loaf with me...but I was off to visit Israel for a week...I should have...I would have eaten better.