Preheat oven to 350 degrees and line a baking sheet with parchment paper.
In a large bowl combine cake mix, eggs, and oil until well combined - mixture will be thick.
Scoop batter onto baking sheet and bake 7-8 minutes.
Cool 5 minutes on sheet before moving to rack.
Frosting:
In a saucepan over medium heat whisk butter, cocoa powder, and milk until butter is melted and smooth.
Remove from heat and whisk in powdered sugar until smooth.
Spoon frosting on each cookie.
Notes
This Recipe Can be Doubled: If you are making these brownie cake cookies for a large gathering or party you can easily double the recipe by proportionally increasing the ingredients to fit your desired yield.
Vanilla Cake Mix: For a slight variation to these cookies, you use can vanilla cake mix to have a chocolate and vanilla cookie.
Add Nuts: To add more a little crunch to the cake like cookies you add nuts like pecans or walnuts.