The recipe makes a mistake in calling for the onion and herbs be used after boiling the pierogi. It's way better to pre-sauté the onion, mix it into the mashed potato together with the herbs (mainly green onion), and shove it in the pierogi.

I also advise to try using hard-boiled eggs by chopping them and putting them in the filling with a generous amount of green onions (this combo can in fact be used on its own, without potato, at least in baked pirozhki). Or alternatively, adding pre-cooked and chopped chicken meat. Fried mushrooms do well too.

You can look up varenyky and chebureki for more inspiration regarding the fillings. E.g. varenyky can be made with cherry or curd. And perhaps also see pirozhki, but those are usually baked.

Thanks so much!

Neat! Thanks!