Place butter in a small saucepan and melt over medium-low heat. Set aside.
Place egg yolks, ½ tablespoon water and lemon juice in a heat-safe bowl. Set up a double boiler by placing a few inches of water in a medium saucepan that the bowl fits well on. Make sure the water does not hit the bottom of the bowl. Bring the water to a simmer and set the bowl on top. Cook, whisking the egg yolks constantly for 5 to 7 minutes, or until the egg yolks begin to thicken and ribbon on themselves when you hover the whisk over the bowl.
Slowly start adding the melted butter into the egg yolks, whisking constantly to keep the emulsion stable. Continue, adding a little butter at a time, until all of the butter has been incorporated and the sauce is smooth and creamy. Remove from heat and season with salt and pepper. Serve immediately.
Notes
Storage: Hollandaise is best enjoyed right away. If you must, you can store it in the fridge for up to 1 day and reheat in the microwave at 10-second intervals until warmed through.Tips: Separate egg yolks from whites while cold. Although using room temperature ingredients is essential to help them emulsify better, it's easier to separate the egg yolks from the whites when the eggs are chilled. Then set the bowl of egg yolks aside to let them come to room temperature.Watch the heat. Keep the heat on medium-low, constantly whisking the egg mixture, and make sure the bottom of the bowl does not touch the water in the double boiler. Keeping the eggs over gentle heat will prevent them from curdling and becoming scrambled.Don't rush the butter. The key to success is to make sure you add the butter a little at a time to temper them, whisking constantly. Adding too much at once may break the sauce.