Wash, clean and shake the chard dry. Cut the white and green parts separately into pieces. Heat butter in a pot. Steam the white part of the chard for about 10 minutes at medium heat. Add 2 tablespoons of water and the green part of the chard and continue cooking for about 2 minutes until the leaves have fallen together. Season to taste with salt, pepper and nutmeg
Mix flour and 50 ml milk until smooth. Bring 150 ml milk to the boil. Add the flour and simmer for 5-8 minutes while stirring. Season to taste with salt, pepper and nutmeg. Remove sauce from the heat and stir in crème fraîche
Grate cheese. Cut ham into strips. Put half of the béchamel in a greased ovenproof dish. Spread chard and ham on top. Pour the rest of the béchamel sauce over it and sprinkle with gruyère and parmesan. Bake gratin in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 25 minutes until golden brown