Cut the ham into small cubes. Wash and peel the potatoes. Clean and peel the kohlrabi. Reserve the kohlrabi greens. Thinly slice the potatoes and kohlrabi on a mandolin.
Wash the kohlrabi greens, shake dry and finely chop.
Mix the potatoes, kohlrabi, kohlrabi greens and ham and season with salt, pepper and freshly grated nutmeg.
Grease a baking dish with butter and add the potato and kohlrabi mixture. Whisk the milk with the cream and pour over.
Grate the cheese and scatter over the potato and kohlrabi mixture. Bake in a preheated oven at 400°F (350°F fan, gas 6) for 45 minutes.
Meanwhile, wash the cucumber, pat dry and cut into thin slices.
Peel and finely dice the onion. Juice the lemon. Wash the dill, shake dry and finely chop the leaves.
Stir 1-2 tbsp lemon juice with the oil and yogurt. Mix in the dill, onion cubes and cucumber slices. Season with salt and pepper and serve with the baked potato and kohlrabi.