Usually chicken in aspic. Supermarkets (more in some regions than others) sell it powdered in sachets (better than gelatine) that work much the same as the ones in the shops in Poland.
It used to be popular years ago, especially in the countryside where they had the bones to get the jelly from, back in the days before fridges and freezers.
Potato, egg, sausage, chive or spring onion - all fried.
Reminds me of shakshuka. Not the kind in the cook books with tomato but the kind people make at home in North Africa.