Thoroughly remove fat and tendons from the leg of lamb with a small, sharp knife. Wash the meat and dab dry. Peel garlic cloves, press them through the garlic press or chop them very finely.
Mix 2 tablespoons of olive oil, garlic, herbs of Provence, salt and pepper with a whisk. Spread the leg of lamb with the herb marinade all around. Leave to stand for about 15 minutes.
Heat the remaining oil in a frying pan. Add the meat and fry until brown all around. Then roast in a preheated oven (electric cooker: 200 °C/ gas: level 3) for approx. 2 hours. Clean, wash and coarsely chop the soup greens.
After 1 1/2 hours roasting time, add to the leg of lamb and roast briefly. Add the wine little by little. Wash the mushrooms and carefully unscrew the stems. Peel onion. Finely dice onion and stems.
Heat the fat in a frying pan. Sauté diced mushrooms and onions in it. Season with salt and pepper. Wash and finely chop the parsley. Mix with the cream cheese. Fill the mushroom-cheese mixture into the mushroom heads.
Remove the leg of lamb from the roaster and keep it warm. Bake the mushrooms in the switched off hot oven for about 10 minutes until the cheese melts. Pour the roast stock through a sieve into a pot, bring to the boil.
Sprinkle in sauce thickener. Bring to the boil again briefly and stir in the cream. Season to taste with salt and pepper. Arrange the leg of lamb and the mushrooms on a plate. Garnish with herbs.
Add the sauce on the side.