Clean and wash the leeks and cut each stem to about 18 cm length. Blanch the leek in boiling salted water for about 4 minutes and drain well
Finely grate the cheese. Melt butter in a pot. Stir in flour and sweat briefly. Add stock and cream while stirring. Bring to the boil, boil for 3-5 minutes. Stir in 75 g cheese, season with salt and pepper. Cut ham in half lengthwise
Spread the leek sticks on an oiled fat pan. Pour cheese sauce over it, sprinkle with the remaining cheese and spread ham on top. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 20-25 minutes. Take out and arrange on 4 plates