Preheat oven to 350 degrees F. Prepare cake batter and bake in mini muffin pan ~11 min. Cool in pans 10 min. Remove to wire racks; cool completely.
Beat milk and dry pudding mix with wire whisk 2 min. or until well blended. Let stand 5 min. Meanwhile, use serrated knife to cut cupcakes horizontally in half. Gently stir 1 cup of the whipped topping into pudding. Spoon about 1 Tbsp. of the pudding mixture onto bottom half of each cupcake; cover with top of cupcake.
Microwave remaining 1 cup whipped topping and the chocolate in small microwaveable bowl on HIGH 1-1/2 min. or until chocolate is almost melted, stirring after 1 min. Stir until chocolate is completely melted and mixture is well blended. Let stand 15 min. to thicken. Spread onto cupcakes. Refrigerate at least 15 min. before serving. Store leftovers in refrigerator.
