> Vatrushka (Belarusian, Russian and Ukrainian: ватрушка) is an Eastern European pastry (pirog) formed as a ring of dough with quark in the middle, sometimes with the addition of raisins or bits of fruit. The most common size is about five inches in diameter, but larger versions also exist. Vatrushkas are typically baked using a sweet yeast bread dough. Savoury varieties are made using unsweetened dough, with onion added to the filling.
Never seen a vatrushka with onions in my life and I'm pretty sure no one I know would ever call a pastry with onions a "vatrushka". It's all about quark and raisins, even a round shape doesn't really matter that much anymore. I mean, show that onion-filled open-top pastry thing to about anyone Russian-born — they'll just say it's some kind of "пирожок", hardly anybody would call it a vatrushka. Show them that specific oven-cooked quark-and-raisins dish of any form — they'll most likely say it's a vatrushka. So, by definition of a language — it kinda is.
By the way, onions are not mentioned neither in Russian or Ukrainian wiki-pages.
https://en.wikipedia.org/wiki/Vatrushka