In a stainless steel bowl set over a pot of simmering water on medium heat, whisk the egg yolks with the lemon juice, water, creole mustard and parsley, together. Season with salt and cayenne pepper, to taste. Whisk the mixture until pale yellow and slightly thick.
Remove the bowl from the pot and whisking vigorously, add the butter, 1 teaspoon at a time, until all is incorporated. Fold in the caviar and serve warm.