In a heatproof bowl, whisk together the egg yolks, water, and lemon juice until well combined.
Place the bowl over a pot of barely simmering water, creating a double boiler. Ensure the bottom of the bowl doesn’t touch the water.
Whisk the egg yolk mixture continuously while slowly pouring in the melted butter in a thin, steady stream. Keep whisking until the sauce thickens and emulsifies, about 5-7 minutes.
Once the sauce has thickened, remove from heat. Season with salt, pepper, and optional cayenne pepper or hot sauce.
Serve immediately or keep warm until ready to serve.