Wash the meat, dab dry and rub with salt and pepper. Place meat on the fat pan of the oven and roast in the preheated oven (electric: 175°C / gas: level 2) for approx. 1 1/2 hours.
After about 20 minutes pour on the stock. In the meantime peel and wash the potatoes and cook them in boiling salted water for about 20 minutes. Peel and wash kohlrabis and carrots. Cut carrots into slices. Quarter kohlrabis and cut into slices.
Cook the vegetables in little salt water for about 15 minutes. Add the peas about 5 minutes before the end of the cooking time. Wash the herbs and chop finely. Remove meat and keep warm. Remove the meat from the fat pan, pour into a saucepan, bring to the boil and add cream.
Stir in the sauce thickener and bring to the boil again. Season to taste with salt and pepper. Stir the herbs, except for 1 tablespoon, into the sauce. Let the fat foam up. Drain potatoes and vegetables. Arrange meat, vegetables and potatoes on a plate.
Pour fat over the vegetables. Sprinkle with remaining herbs. Pour some sauce over the meat. Garnish with chervil. Add remaining sauce extra.