Cook sugar in a dry heavy saucepan over moderate heat, undisturbed, until it begins to melt. Continue to cook, stirring occasionally with a fork, until sugar is melted into a deep golden caramel. Remove from heat and carefully add cream in a slow stream (mixture will bubble and steam). Return to low heat and cook, whisking, until smooth.
Stir together 1/2 cup milk and cornstarch. Beat eggs, vanilla, and salt in another bowl.
Stir remaining 2 1/2 cups milk into caramel and bring to a simmer, whisking occasionally. Stir cornstarch mixture, then whisk into caramel. Bring to a boil, whisking, and simmer, whisking, 2 minutes, then remove from heat.
Whisk about 1 cup hot caramel mixture into egg mixture until well blended, then whisk egg mixture back into caramel. Continue whisking off the heat for 1 minute.
Whisk 1/2 cup hot caramel pudding into chopped chocolate, stirring until smooth. Spoon chocolate pudding into 6 (8-ounce) parfait glasses, then top with caramel pudding. Chill until set, at least 3 hours.
Pudding can be made up to 3 days ahead and chilled, covered with plastic wrap.;
Recipe courtesy of Gourmet Magazine