Drain the mozzarella and cut into 4 slices. Wrap a slice of ham around each piece. Peel, wash and coarsely grate the potatoes. Stir in eggs and flour. Season with salt and pepper. Heat the oil in a large coated pan over a low to medium heat. Form 4 Rösti with your hands out of half of the potato mixture, put some potato mixture in one hand, put a piece of wrapped cheese on each, cover with the rest of the potato mixture and press down carefully. Pour the potato mixture into the hot oil and fry over medium heat for 8-9 minutes, turning. Keep Rösti warm in the preheated oven (electric cooker: 150 °C/ convection oven: 125 °C/ gas: see manufacturer)
In the meantime, peel garlic and chop finely. Peel and finely chop the onion. Clean and wash the chard. Cut stalks and leaves separately into pieces. Wash and halve the tomatoes. Heat butter in a pot. Brown onions and chard stems in it. Stir 3 tablespoons of stock with starch until smooth. Deglaze the chard with the remaining stock. Stir in crème fraîche and starch mixture. Simmer for 3-4 minutes at low heat. Add chard leaves and tomatoes. Let simmer for 1-2 minutes more. Season to taste with salt, pepper and nutmeg
Arrange potato rösti with cream chard and tomatoes on plates