Wash, peel and coarsely grate the potatoes. Mix potato flour and egg, season with salt, pepper and nutmeg. Fold over half of the ham slices and place 1 slice of cheese between each slice.
Coat ham pockets approx. 1/2 cm thick with potato dough, press on well, turn and coat the other side with dough as well. Press the potato pancakes well. Heat 2 tablespoons of oil in a coated pan.
Fry the cordon bleu in it for about 4 minutes on each side. Sprinkle with hazelnuts. Meanwhile clean, wash and coarsely dice the tomatoes. Peel and chop onion and garlic. Heat the remaining oil in a pot.
Fry the onion and garlic until transparent. Add the tomatoes and stew for about 5 minutes. Wash the basil and chop finely, except for a little to garnish. Stir basil into the tomatoes and season with salt and pepper.
Arrange cordon bleu with tomato vegetables. Garnish with remaining basil leaves.