Rheinhessen expression for a special type of onion cake typical for Rheinhessen, even though it is not originally from there. There are many different version of this and no Zwiwwelkuche tastes like the other, as everyone has their own recipe. It probably is most comparable to a French Quiche Lorraine, but replacing the eggs with onions. The basic rule is: base of salty yeast dough, topped with small bacon cubes, steamed onion rings and sour cream. It is eaten oven-warm and combined with a fresh Federweißer. Delicious!
Here you can find the traditional recipe for Zwiebelkuchen (in German only)