Clean and wash the leek and cut rings. Heat the fat in a saucepan. Sauté the leek rings in it. Take out 2 tablespoons of leek and set aside. Deglaze the leek with the broth, bring to the boil and cook for 10 minutes. Cook spaetzle in boiling salted water for 2 minutes and drain.
Drain the bacon in a pan. Puree leek in the stock, refine with cream. Season to taste with salt and pepper. Add leek rings and spaetzle to the soup and warm up. Serve leek soup with bacon cubes