Wash the meat, dab dry and season all around with salt and pepper. Place on the fat pan of the oven and bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for approx. 1 hour.
25 minutes before the end of the cooking time, cover with bacon and pin the ends with wooden sticks. In the meantime, peel, wash and quarter the potatoes. Heat oil in a pan and fry the potatoes for 12-15 minutes until golden brown.
Peel and wash kohlrabi and carrots and cut into slices and pieces as desired. Cook in salted water for 8-10 minutes and then drain. Remove wooden sticks from the roast. Let the roast rest.
Heat butter. Pluck the chervil leaves from the stalk and add to the butter. Cut the roast into slices and arrange on a plate together with the vegetables. Pour chervil butter over the vegetables and serve garnished with lemon slices and chervil as desired.