- Preheat oven to 400 degrees. Spray 12 nonstick muffin cups with nonstick baking spray containing flour and set aside.
- In a medium microwave-safe bowl, combine both kinds of chocolate chips and butter. Microwave on high power for 1 minute, stirring twice during cooking, or until chocolate and butter are melted and mixture is smooth. Cool for 5 minutes.
- In a large bowl, combine eggs and egg yolks and beat at high speed for 5 minutes until foamy, light in color, and doubled in size.
- If there is one, set aside the chocolate syrup packet from brownie mix. Gradually add the dry brownie mix to the beaten egg mixture, stirring with wooden spoon until well blended. Fold in melted chocolate mixture and chocolate milk. Carefully pour batter into prepared muffin cups.
- Bake at 400 degrees for 10 to 14 minutes or just until edges are set. The centers of the little cakes will be soft. Cool on wire rack for 2 minutes. Then run a knife around edge of each cake to loosen, then invert warm cake on each serving plate.
- Drizzle with the chocolate syrup from the reserved packet and sprinkle with powdered sugar. If there isn't a chocolate syrup packet in the brownie mix, drizzle the cupcakes with some chocolate ice cream topping.
