Peel onions and garlic, chop garlic finely. Cut the meat into pieces and put it in a plastic bag with flour. Season with salt, pepper and mustard powder. Shake the bag so that the meat is covered on all sides with spices and flour
Heat the oil in a frying pan and fry the meat in 2 portions over high heat on all sides. Add the onions and fry for another 2 minutes. Deglaze the roast with red wine, bring to the boil and reduce for about 2 minutes. Season with garlic. Add stock, bring to the boil
Crush the juniper and allspice in a mortar and add to the roaster with the redcurrant jelly. Cover and cook in a preheated oven (electric cooker: 150 °C/ convection oven: 125 °C/ gas: see manufacturer) for approx. 1 hour. Clean and clean the mushrooms and halve them depending on size. Add chestnuts and mushrooms and cook for another 1 1/2 hours until the meat is tender. Season to taste and serve immediately