Boil water in a pan, add salt and spinach and cook for 1 minute or until wilted. Drain the spinach, squeeze, chop and set aside.
Heat butter in a saucepan, add chopped onion and garlic and cook for 3 minutes or until fragrant. Add cream cheese and heavy cream and cook until smooth.
Add chopped spinach and simmer for 10 minutes. Season with nutmeg, salt, and pepper.
Preheat the oven to 400 F.
Transfer spinach to the baking dish and make small hollows in the spinach with the back of the spoon.
Crack an egg into each hollow.
Bake up to 15 minutes or until egg whites are set.
Season casserole with salt and pepper. Serve sprinkled with grated Grana Padano cheese.