1. Preheat an oven to 375 degrees F.
2. Heat a large frying pan over medium heat. Add the butter and lightly fry onions and broccoli until soft.
3. Lightly spray a glass baking dish to prevent sticking. Add the broccoli and onion mixture. Then add in the whisked eggs + egg whites. Combine and spread evenly. Then add the cheddar cheese. Season with salt and pepper.
4. Bake for about 25-30 minutes (cooking times will vary). If you are eating right away you will want it to be firm and ready to eat. If you are prepping for the week it is okay to slightly under cook to prevent it from getting too rubbery when reheated. As the egg bake cools it will tighten up. You will know it is not done when there is a lot of liquid in the centre.