In case you mean onion confit, I have, and it is jummy. Here is the first recipe I found on the net, observe that it requires almost no sugar (actually, I usually leave it out completely, like the caraway seeds, I think they are superfluous).
A brief excursion into the realm of terminology: What you call marmalade we call marmalade too in other European languages (vocals may vary: mermelada in Spanish, Marmelade in German and so on). Its origin is Portugese, the word marmeleiro means quince, the fruit you can not eat raw. It is a good name for the preserves, I believe, it may have been the original fruit that was boiled with sugar to make it edible. But quinces are not citrus fruits, and so the rest of the world calls any preserve boiled with sugar marmalade, while when you say marmalade in English you mean orange, lime, lemon… but no berries. That you call jam. Other languages don’t distinguish between jam and marmalade.
And then there are jellies and compote and what is called Apfelmus (or Apfelkompott or Apfelbrei) in German you call apple sauce. There are probably even more words for those recipes which are basically the same, people pay atention to those details when it comes to cooking and eating.