A regular yellow onion can be substituted for the sweet onion.
The onion filling can be cooked, covered and refrigerated up to 24 hours ahead. Just before serving, assemble appetizers and bake as directed.
Sprinkle some chopped fresh parsley on top of these puffed bites. Add a few sprigs of fresh marjoram and sliced grape tomatoes to the serving platter for an instant touch of holiday.