For the Mug Cake, microwave chocolate chips and butter in microwavable coffee mug on HIGH 30 seconds or until melted. Stir. Add remaining ingredients; mix well.
Microwave on HIGH 45 seconds to 1 minute or until center looks almost set. Let stand 5 minutes before serving.
Meanwhile, for the Topping, mix cream cheese and confectioners’ sugar until well blended. Stir in milk. Drizzle over mug cake.