Melt butter in a large frypan over medium high heat. Saute capsicum and mushrooms until tender then stir in stock and flour. Cook stirring until thickened. Add chicken, heat through and remove from heat.
In a small bowl combine sour cream, egg yolks, sherry, salt and pepper then mix together.
Add the sour cream mixture to chicken mixture in frypan and heat thoroughly stirring. Serve hot.