In a heatproof bowl, whisk together the egg yolks and water.
Place the bowl over a pot of simmering water (double boiler) and whisk continuously until the mixture thickens.
Slowly drizzle in the melted butter while whisking constantly until the sauce has emulsified.
Remove from heat, whisk in lemon juice, salt, basil, and cayenne pepper.
Adjust seasoning to taste and serve.