This rich and creamy dessert can either be chilled in a large bowl or divided into individual containers. Top this recipe with sweetened whipped cream to help balance the bittersweet chocolate flavor.
In a medium-size heavy-bottomed saucepan, whisk together the sugar, cornstarch, cocoa powder and nutmeg. Gradually add milk, whisking constantly to keep mixture from getting lumpy.
Transfer saucepan to stovetop, and heat over medium heat, stirring constantly with a wooden spoon. Bring to a boil (about 10 minutes), then boil 2 minutes.
Remove from heat and add chopped chocolate. Stir until all pieces are melted. Stir in vanilla. Strain into a large bowl, then either cover surface with plastic wrap or divide into individual cups and cover. Refrigerate until cold, about 2 hours. Serve with whipped cream or whipped topping, dusted with cocoa, if desired.