Preheat oven to 350 degrees F.
Line an 8x8 baking pan with parchment paper and spray with cooking spray.
(This makes it easier to lift bars out of pan and cut.)
Mix cake mix, eggs, and oil with a mixer until combined. About 2 minutes.
Bake for 12-15 minutes but be careful not to overcook.
After brownies are cooled, hold the sides of the parchment paper and lift out of pan. (I cut the sides off of my bars)
In a small bowl, mix powdered sugar, vanilla and milk until combined. Pour glaze over bars and spread to the edges.
Let the glaze set about 10 minutes and then cut into squares.