Melt butter in a saucepan. Add curry powder and all-purpose flour, whisking constantly over low heat for 3 minutes. Gradually add stock, whisking until boiling. Reduce heat. Season with paprika and salt. Combine egg yolk and milk. Add to soup, whisking constantly until soup is slightly thickened.
Add chicken and simmer until thoroughly heated. Serve sprinkled with chopped chives.
Note: Yield: 4 Servings, Degree of Difficulty: Easy