Peel and quarter the onion. Boil up plenty of water with onion, juniper berries and bay leaf. Place the brisket in the pan and cook over medium heat for about 45 minutes. Peel, wash and slice the potatoes.
Cook in boiling salted water with caraway seeds for about 15 minutes. Clean the leek, cut in half lengthwise and wash. Drain and cut into pieces. Cook in boiling salted water for about 8 minutes. Drain and let it drain, catching the cooking water.
Heat the fat in a saucepan. Stir in flour. Add cream and 100 ml cooking water while stirring. Let the sauce simmer at low heat for about 10 minutes. Season with salt, pepper, some sugar and nutmeg.
Add the leek. Add chives rolls to the potatoes. Remove the meat from the stock and cut into slices. Arrange a few slices of meat with leek vegetables and potatoes on each plate.