Add your spinach, potatoes and feta into a baking tray.
In a separate bowl mix your eggs, egg whites and milk. Season with salt and pepper.
Top with with shaved Parmesan
Place in the oven for 60 minutes at 180C for the eggs to cook fully. It should swell up a lot as it browns, that's how you know the eggs are cooked.
Slice into four quarters and store to take to work. You can eat it cold or reheated.
