Robert Evans, who recently came out with his book “The Fat Lady Sang,” the sequel to his best-selling memoir “The Kid Stays in the Picture,” is encouraging other authors. We’re told Evans — producer of “The Godfather,” “Rosemary’s Baby,” “Love Story” and “Chinatown”— encouraged his friend Cathleen Smith, a former Helmut Newton model, to write the children’s book “Sassafrass Jones,” and helped come up with the main character, a lovable dog. “Hooray for her . . . for her giving of her mind, her charity and her spirit,” Evans writes on the jacket. The book will be feted Saturday at Verdura, with proceeds going to the Humane Society of New York.