Soak the beef tongue in ice-cold water for about 3 hours. Then place in a bowl. Add the carrots, celery, onions, garlic, bay leaves, ginger, allspice, pepper and juniper berries. Pour the red wine over it and let it steep in the refrigerator for at least 12 hours.
Remove the tongue from the marinade. Drain the vegetables while collecting the red wine. Heat clarified butter in a large saucepan and fry the vegetables in it. Add the tomato paste and roast with it. Deglaze with the red wine and beef stock. Add the cranberries, sugar and leek and bring to the boil.
Put in the tongue, season with salt and cook for about 3 hours, until the tip of the tongue can be pricked very easily with a knife. Take the tongue out of the broth, peel off the skin and cut into approx. 1 cm thick slices. Lightly fry these slices in butter on both sides. Pass the sauce through a sieve, thicken with cornstarch and season to taste.