For the spinach lasagna casserole, first sort out the spinach, trim the hard stems and rinse the leaves thoroughly. Melt 25 g of butter in a large saucepan.
Add the spinach, dripping wet, and steam until soft and no water remains. Season with salt, pepper and grated nutmeg. Cook the lasagna sheets in enough bubbling hot salted water, to which a generous dash of oil has been added, until al dente (firm to the bite), about 10 minutes. Drain and place one against the other on a kitchen towel.
Peel the onions and garlic and fry them in the remaining butter until golden. Finely dice both types of ham and add. Stir-fry for about 3 minutes. Drain the tomatoes and chop coarsely. Grease an ovenproof dish and start with a layer of lasagne sheets. On top, alternate layers of ham mixture, spinach, pasta and tomatoes. Season each layer of tomatoes with salt, pepper and oregano. The final layer should be lasagna sheets. Mix the cheese with beaten eggs and sour whipped cream. Spread over the lasagna.
Bake in the oven at 180° for about 40 minutes, until the lasagna has a golden brown color. Bring the spinach lasagna casserole to the table.