In a heavy saucepan, combine sugar, cornstarch and salt. Gradually add cream and milk. Bring to a boil over medium-high heat, stirring constantly. Reduce heat; cook and stir with a wire whisk 2-3 minutes more or until thickened.
Remove from the heat. Stir 1-1/2 cups hot mixture into egg yolks; return to saucepan. Stirring constantly, bring to a gentle boil; cook and stir 2 minutes more. Remove from the heat; stir in chips until melted. Stir in extract.