Wash and drain sorrel; shred finely. Simmer gently in butter until soft. Add chicken consommé and bring to a boil.
Combine egg yolks, double cream, and salt and freshly ground black pepper, to taste, in a large mixing bowl, and whisk with an egg beater until smooth. Pour hot consommé on to the egg mixture and mix well. Pour mixture into a clean saucepan and simmer gently over a very low heat, stirring constantly, until smooth and thick. Do not let soup come to a boil, or it will curdle.