In a medium saucepan, whisk together skim milk, sugar, coca powder, cornstarch and Sweet ‘N Low. Whisking constantly, cook 6-8 minutes, until mixture boils and thickens. Remove saucepan from heat. Stir 1/4 cup milk mixture into beaten eggs, stirring constantly to avoid curdling. Pour egg mixture back into saucepan and stir in extract. Cook, stirring constantly over low heat, 2-3 minutes or until custard thickens; do not let custard come to a boil. Pour custard into individual dessert cups or a serving bowl and cover with plastic wrap. Refrigerate for at least 2 hours before serving.