Spray an 8x8-inch pan with nonstick cooking spray or line with parchment paper. Parchment Paper will make it much easier to slice and serve. Preheat oven to 350F degrees.
Mix together dry cake mix with butter and eggs using an electric hand mixer, then stir in chocolate chips by hand. Batter will be very thick.
Spread batter into prepared dish. Bake for about 20-25 minutes or until top is firm and a toothpick insrted comes out clean. Let cool completely before icing.
To make frosting, beat together softened butter, powdered sugar and milk with an electric hand mixer, until thick and creamy.
Once bars are cooled, spread frosting out in a thick layer on top.
Cut into squares before serving.
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Notes
This recipe can be made with any flavor of boxed cake mix.