Peel, wash and roughly dice the potatoes. Cook in salted water for about 10 minutes. Drain and put aside. Peel kohlrabi and cut into sticks. Cook in boiling salted water for 4-5 minutes, drain and quench.
Clean, wash and halve the leek and cut into wide diagonal strips. Dice the smoked pork. Heat oil in a pan. Fry the meat on all sides until golden brown. Add the leek and fry briefly.
Mix the potatoes, kohlrabi, leek and celery and place in a greased casserole dish. Peel the garlic and press it through a garlic press. Beat the garlic, sour cream, eggs and milk. Season vigorously with salt, pepper and nutmeg.
Pour casting over the casserole and cook in the preheated oven (electric cooker: 175 °C gas: level 2) for approx. 40 minutes. Wash the rosemary and dab dry. Pluck the needles and chop finely. Melt the fat in a pan.
Add breadcrumbs and rosemary, season with salt and pepper. Add to the casserole 10 minutes before the end of the cooking time.