Bring approx. 21/2 litres of water to the boil in a large pot. Peel onion and carrot and cut into pieces. Add to the water together with the bay leaves, peppercorns and cloves. Wash the roast and put it into boiling water. Cook on low heat for about 11/2 hours.
In the meantime peel, wash and drain the potatoes. Heat oil in a pan and fry the potatoes in it at medium heat for 15-20 minutes until golden brown all around. Season with salt and pepper. Peel the carrots, leaving a little green, and wash them. Clean, peel and slice the kohlrabi. Cook carrots and kohlrabi in boiling salted water for 10-12 minutes, drain. In the meantime mix salad cream and yoghurt, season with salt and pepper. Chop chives and chervil finely and stir into the yoghurt cream, except for a little chives. For the roast, wash the parsley, dab dry, pluck the leaves from the stalks and chop finely. Melt the fat.
In the meantime mix salad cream and yoghurt, season with salt and pepper. Chop chives and chervil finely and stir into the yoghurt cream, except for a little chives. For the roast, wash the parsley, dab dry, pluck the leaves from the stalks and chop finely. Melt the fat. Add mustard, parsley and remaining chives and mix. Remove the roast, let it rest for a while and brush it with the parsley sauce. Arrange roast, roast potatoes and vegetables together with the herb cream on a plate and serve garnished with chervil if desired