Parboil the cleaned spinach in a little salted water, drain it and divide into two parts. Cut the ham into cubes and fry briefly in hot oil. Place half of the spinach in an ovenproof dish, arrange it with ham and pour with one half of the sauce quantity. Put the remaining spinach, pour in the remainder of the sauce and place on top of it the cheese, cut into slices. Bake in an oven.
Fry lightly the chopped onion in hot butter, add the flour and pour in the milk. Mix well, add salt, pepper, nutmeg and cook briefly until you get a thin porridge.