Peel and chop the onions. Fry them until they become transparent using oil.
Whisk the milk with eggs in a bowl.
Add the tomatoes, ham, grated cheese and onion.
Season with salt and pepper, and sprinkle with grated nutmeg to taste. Mix it all well.
Heat the oil in an oven-proof pan on the stove. Pour in the egg mixture and cook for 5 minutes.
Arrange the asparagus on top of the omelette, and put in the oven for 15 minutes, so that the omelette rises. Keep an eye on it, to prevent it from burning.