Bring a pot of salted water to a boil. Add the broccoli florets and cook, uncovered, for just 1 minute. Turn off the heat, drain into a colander and immediately place the broccoli in the ice bath to stop the cooking process for 30 seconds. Drain the broccoli again in the colander.
In a large mixing bowl, combine broccoli, soup, lightly beaten eggs, melted butter, onion, salt, pepper, mayo, and sour cream. Mix well.
Add a cup of shredded sharp cheddar cheese and mix well.
Transfer to a large greased baking dish and cook, uncovered, for about 30 minutes.
Remove the casserole from the oven, add about 1/2 cup cheddar cheese on top along with some fried onions.
Put the casserole back into the oven and continue cooking until the top cheese is melted (for about 10 minutes).