Add the egg:
Let the egg cook for a few minutes: Let the egg gently cook without moving it. The whites will start to set after a few minutes, followed by the yolk.
Cook the top of the egg: To be sure the whites are totally set on a sunny-side-up egg, you can cover the pan partway through cooking. The steam from the egg and the butter will gently cook the top. You can also flip the egg over and cook for a minute on the other side. This turns a sunny-side-up egg into an over-easy egg!
Remove from heat and eat: When the whites are set and the yolk is done to your liking, remove the pan from heat. Gently slide the spatula under the egg and transfer it to a plate. Eat immediately.