Wash the meat, dab dry and season with salt and pepper. Heat the oil in a roasting pan and fry the meat in it. Peel and halve onions and add them to the meat with bay leaves and peppercorns.
Add wine and 1/4 litre of water, bring to the boil and cook over medium heat for two hours. In the meantime, clean, wash and halve the mushrooms. Clean the leek, wash and cut into rings.
Clean, wash and slice the tomatoes. Heat the fat in a frying pan, sauté the mushrooms, add the leek and fry for five minutes while turning. Stir in tomatoes and season with salt and pepper.
Wash the thyme, keep some for garnishing, chop the rest finely. Sprinkle the chopped thyme over the vegetables. Keep vegetables warm. Remove the roast. Stir the sauce thickener into the roast stock, bring to the boil again.
Season to taste with salt and pepper. Cut the meat into slices and arrange on a plate with the vegetables. Pour some sauce over the meat slices, sprinkle with pepper and garnish with the remaining thyme.
The rest of the sauce extra is fine.