Chop the vegetables. Pour the chicken broth into a medium sized saucepan. Add the vegetables and bring to boil. Lower the heat and simmer, uncovered for 45 min. Strain the vegetables. In a small bowl mix the cornstarch and water to form a paste. Stir into the broth and cook until slightly thickened. Add the cheese and cook until the cheese melts. Add the white pepper, nutmeg and salt to taste. In a small bowl, whisk the egg yolk into the cream. Stir in 1/2 cup of the soup and mix well. Add to the soup, stirring rapidly. Cook for 2 minutes, being careful that is does not boil Top with chopped chives for garnish and serve.