Chef John's Easy One-Bowl Hollandaise Sauce
Place egg yolk into a large stainless steel bowl. Whisk in water, lemon juice, salt, and cayenne pepper. Add butter cubes. Place bowl over low heat. Whisk continually until butter melts and mixture gets foamy, about 3 minutes. Continue whisking over low heat until sauce is to your desired thickness, 3 to 5 more minutes.Advertisement
You can also use a double boiler to make the sauce.
If sauce gets too thick, just thin it with a little hot water.