Melt the butter or margarine in a saucepan. Add the curry powder and flour, whisking constantly over low heat for 3 minutes. Gradually add stock, whisking until boiling. Reduce the heat. Season with paprika and salt. Combine the egg yolk with milk. Add to the soup, whisking constantly until the soup is slightly thickened. Add the chicken and simmer until thoroughly heated. Serve sprinkled with chopped chives. Serves 4