Cut the onions into rings and the apple into pieces, fry in the pan until the onions are golden yellow. Then move the onions to one side and let the sugar caramelize in the open space. When the sugar is ready, stir everything again. Season with salt.
In the meantime, coat a baking dish with butter. Put in the dumplings and cover with the onions. Then sprinkle the cheese on top.
Bake in a preheated oven (180 ° C) for 20 minutes, but sprinkle with pepper beforehand.