Clean, wash and cut the leek into rings. Cover and steam in little boiling salted water for about 2 minutes, drain
Cut 150 g cheese into slices. Cut the ham and cheese into slices of approx. 4 x 4 cm each. Peel and chop onion. Peel the potatoes and cut or slice them thinly
Grease a large casserole dish (28 cm Ø) and sprinkle with onion. layer potatoes, leek, ham and cheese slices fan-shaped
Season cream and milk with salt and pepper, pour over the casserole. Grate the rest of the cheese over the casserole. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/gas: level 2) for approx. 50 minutes until golden brown. Garnish if necessary