Add cake mix and powdered sugar to a microwaveable bowl. Mix together.
Add in butter and milk. Do not mix. Microwave for 2 minutes on high.
Remove from microwave immediately and stir together to combine. Stir in mini chocolate chips.
Immediately spread the batter in an 8-inch greased baking pan. Add a few mini chocolate chips to the top and press down with the palm of your hand or a spoon to set in place.
Refrigerate for 2 hours or until set. Cut into squares and enjoy!
Notes
I like Betty Crocker Super Moist Devil's Food Cake mix.