How to Make It
In a saucepan, melt the butter. Add the leeks and cook over moderate heat, stirring, until softened, 3 minutes. Add the broth and rice, cover and cook until the leeks and rice are tender, 15 minutes. Stir in the parsley, tarragon and chives; bring to a boil.
In a blender, combine the egg, yolk and cream. With the machine at low speed, carefully pour in the soup, blending until smooth. Return the soup to the saucepan, season with salt and pepper and heat just until warm. Transfer to bowls and serve.