Dice the onion and fry in a pan with a little butter. Add the bacon cubes and fry them. Then put everything in a pan suitable for the oven and fry the sauerkraut in a little fresh butter in the same pan. Then also put the sauerkraut in the mold. Finally, fry the spaetzle and add to the remaining ingredients in the mold. Mix everything together and let it steep in the oven at approx. 150 ° C for 15 minutes.