In medium pan, mix sugar, cornstarch and salt. Gradually stir in half and half. Cook and stir over medium heat til mixture comes to a boil and thickens. Boil for 2 minutes and remove from heat. Stir 1/4 cup of mixture in pan into beaten egg yolks, then stir egg mixture into saucepan. Cook 2 more minutes. Stir constantly. Remove from heat and add vanilla. Cool for 10 minutes stirring occasionally. Cover and refrigerate.