Clean, peel, quarter and slice the kohlrabi. Peel, wash and slice the potatoes. Cook both in boiling salted water for about 10 minutes. Wash the meat, dab dry. Cut into strips.
Heat oil in a pan. Fry meat until golden brown, turning. Season with salt and pepper. Drain potatoes and kohlrabi, let drain. Layer vegetables and meat in 2 layers in a round, greased casserole dish (22 cm Ø). Mix cream and flour. Season with salt, pepper and nutmeg, pour over the casserole. Sprinkle with cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 30 minutes. Wash, clean, quarter and core the tomato.
Season with salt, pepper and nutmeg, pour over the casserole. Sprinkle with cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 30 minutes. Wash, clean, quarter and core the tomato. Cut into small cubes. Sprinkle over the gratin. Serve garnished with marjoram