Cut the onions into cubes and sauté in oil until translucent. Allow to cool slightly.
Knead the flour with yeast, salt and sugar well (approx. 5 min.). Then add the onions and fried onions and mix everything well. Put the dough in a large floured container with a lid and let it rise in the refrigerator for about 10 to 12 hours.
Preheat the oven to 240 ° C.
Place the dough on a floured work surface (do not knead any more) and cut into 3 equal parts and turn 2 to 3 times. Then place on a baking sheet with parchment paper. Then bake the whole thing on the middle rack for 30 minutes. The first 15 minutes at 240 ° C and the remaining 15 minutes at 220 ° C.