Cut off the roots and dark green leaves from the leeks. Wash the leeks thoroughly. Halve each stick once across and pre-cook in plenty of boiling salted water for about 8 minutes. Then rinse in cold water and drain well.
Halve the ham slices lengthways and wrap half a slice of ham around each of the leeks. Preheat the stove to 200 degrees (no convection).
Heat the butter in a saucepan and sweat the flour in it. Pour in the milk while stirring vigorously and simmer for about 5 minutes, always stirring. Cut off the outer layer of white mold from the cheese, chop it up and let it melt in the sauce. Season to taste with a little salt, pepper and lemon juice.
Grease a square, flat casserole dish, put in pieces of leek and pour cheese sauce over it. Bake in the middle of the oven for 20-25 minutes (gas mark 3). Scatter the Appenzeller over the top about 10 minutes before the end of the baking time.
Roast the hazelnut leaves in a pan until golden brown and sprinkle over the leek before serving. Baguettes, toasted white bread and mashed potatoes are suitable as side dishes, and white wine, e.g. Riesling, as a drink.