Peel, wash and slice the potatoes. Cook in plenty of boiling salted water for about 8 minutes until al dente. Drain potatoes and rinse with cold water. Peel, wash, quarter and slice the kohlrabi.
Peel, wash and slice the carrots diagonally. Wash, clean and slice the leek diagonally. Steam kohlrabi, carrots and leek one after the other in a closed pot with little water for about 6 minutes until al dente and chill.
Mix eggs and milk, season with salt and pepper. Layer the vegetables in a ring shape in a greased casserole dish. Pour the egg milk evenly over it. Allow to set in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 45 minutes.
Garnish with parsley.