Wash the pumpkin, clean, cut in half, core and cut into 12 wedges. Wash, clean, cut into rings, put in boiling water for 1 minute. Drain and drain well.
Preheat the oven to 200 degrees (convection 180 degrees).
Heat the butter in a saucepan. Add flour, sweat briefly while stirring. Stir in cream, add milk and juice. Bring to the boil while stirring, season with salt, pepper and nutmeg.
Wrap the ham around the pumpkin slices, place in 4 greased casserole dishes (each about 12 cm, alternatively 1 casserole dish with 25 cm). Mix the leek with the sauce and 75 g cheese and pour over it. Sprinkle with the remaining cheese, bake in the oven for 30-35 minutes.