Peel the potatoes, boil them in salted water and press or mash them through the press. Stir in 2 egg yolks, poppy seeds and parmesan, add a little starch if necessary and season with pepper, nutmeg and salt. Form dumplings from the mass.
Clean the leek, cut it into small pieces and sweat it in butter. Now press a hole in the dumplings, add a little leek and seal the dumplings. Let it steep in boiling salted water for about 15 minutes.
In the meantime, fill up the remaining leek with cream, season and, if necessary, thicken with a little starch. Serve the dumplings with the sauce.