Cook the potatoes as cooked, peeled just.
Clean and rinse the leeks. Cut into 3 cm long pieces and cook in salted water until just done, drain, rinse and drain well.
Cut ham into 1 cm cubes, remove rind from cheese and grate coarsely. Rinse the potatoes, peel and cut into 2 cm cubes.
Preheat electric stove to 200 °C. Grease a large shallow gratin dish. Melt butter or light butter in a saucepan, sweat flour in it, add milk and clear soup, stir heartily and make a few minutes. Season the sauce with pepper, nutmeg and a little salt. Fold in half of the grated cheese.
Place the leek pieces vertically in the mold. Put the diced potatoes and ham in between. Pour the sauce over the leeks, sprinkle with the remaining cheese and bake for 30 minutes (gas: level 3).
Tip: It’s best to use your favorite ham – then your dish will taste twice as good!