Wash the meat under cold running water, pat dry and place in an appropriately sized bowl or glass roasting dish with a lid.
For the marinade, cut the onion at both ends, peel and lard the halves with the cloves. Clean and wash the carrot, celery and leek and cut into large pieces. In a saucepan, bring the water, vinegar and red wine to the boil together with the bay leaves, crushed juniper berries, allspice and peppercorns. Add the onions and the prepared vegetables and bring to the boil once. Take it from the stove and let it cool off. Pour the cooled stain over the meat. Marinate in the refrigerator for at least 1 week, turning twice a day.
Remove the meat from the marinade. Put the stain in a 4 liter saucepan (with a lid) and bring to the boil. Add the salt to the broth, reduce the heat and cook the meat for 2 hours, turning frequently. When the meat is done, remove it from the broth. Strain the broth with a fine sieve and keep it. Gently squeeze the vegetables with a fresh tea towel. Discard the pressed material, bring the collected broth with the stain to 500g and use it for the sauce. Discard the rest of the stain.
For the sauce, melt the butter in a pan, sprinkle with the crumbled gingerbread and sugar. Dust the mixture with flour, stirring constantly, and stir until smooth. Deglaze with the prepared stain and simmer gently for 10 minutes. Season with salt and pepper and stir in the cream.
Cut the meat into slices and heat briefly in the sauce. Place 2 slices on each serving plate with a little sauce. Add side dishes of your choice and serve warm. Serve the rest of the sauce in the sauce pot.