BEAT egg, milk and syrup in large saucepan with wire whisk until well blended. Add tapioca and sugar; mix well. Let stand 5 min.
BRING to full rolling boil on medium heat, stirring constantly. Remove from heat. Stir in walnuts and vanilla.
COOL 20 min. (Pudding thickens as it cools.) Serve warm or chilled. Stir before serving.