In a medium saucepan, thoroughly mix sugar, cornstarch, cocoa powder and instant coffee. Gradually stir in milk until blended. Cook over medium heat, stirring frequently, until mixture thickens and boils. Remove from heat. Stir in vanilla. Pour into serving dishes and cool at room temperature for one hour. Refrigerate until serving time. Metric quantities: 125 ml sugar, 45 ml cornstarch, 45 ml cocoa, 5 ml coffee, 500 ml milk, 5 ml vanilla.