Combine first 4 ingredients, sugar, cornstarch, cocoa and salt in a medium saucepan; stir in milk and egg YOLK. Cook over medium heat, stirring constantly, until mixture comes to a boil; cook 1 additional minute, stirring constantly. Remove from heat, and stir in vanilla.
Pour into 2 individual serving dishes. Serve warm or chilled; top with whipped cream and pecans, if desired. Yield: 2 servings.