Melt butter in a small pot over medium heat.
Bring water in a pot to boil and place a heat-resistant mixing bowl over the water bath.
Add egg yolks, lemon juice, salt and water into the bowl. Whisk the mixture using a whisk continuously.
After 1-2 minutes, remove the pot and bowl from the stove. Using the rest of the heat from the boiling water, continue whisking the egg mixture until it changes colour.
Once the egg mixture turns creamy, add in melted butter slowly to the mixture, starting with a tablespoon of butter. Slowly increasing the amount of butter until you get your desired consistency. Do not add in the residual of the melted butter into the sauce. Whisk sauce until creamy and smooth.
Season ground black pepper according to taste.
Serve warm and immediately. Discard leftover.