For the kohlrabi ham casserole, peel the kohlrabi, save the heart leaves, cut the kohlrabi into thin sticks and bring to the boil in salted water. Boil for 10-15 min (not too soft), drain kohlrabi and collect the liquid.
Knead butter and flour together with a fork, bring kohlrabi liquid to a boil, add flour-butter mixture while stirring throughout with a whisk, bring to a boil again and cook on stove for about 5 min.
Stir in the sour cream, season the chopped heart leaves and kohlrabi sticks with pepper and salt and add.
Dice the cooked ham, layer the kohlrabi and ham alternately in a greased baking dish.
Mix eggs with nutmeg seasoning, season with pepper and salt and pour over the casserole.
Cover the gratin dish with foil and bake the kohlrabi and ham casserole in a preheated oven at 225-250° C for about 30 minutes.