Preheat oven to 350 degrees F.
Spray a 9 x 13 inch cake pan with non-stick spray.
Remove 1/2 cup dry cake mix and place in a medium sized bowl. Set aside.
Add remaining cake mix, butter, eggs and sour cream to Mixer Mate Bowl and beat with electric mixer on medium speed for about 2 minutes. Scrape down the sides if needed.
Pour about half of batter into prepared cake pan, spreading evenly.
Add brown sugar, pecans and cinnamon to reserved cake mix and combined. Sprinkle evenly over cake batter.
Spoon remaining cake batter over pecan mixture and carefully spread evenly.
Bake for 30 to 35 minutes or until cake is cooked through and springs back slightly when touched.
Add powdered sugar, cocoa, milk and vanilla to a medium bowl and whisk to combine.
Poke top of warm cake with a skewer and pour glaze over the top, spreading evenly.
Cool completely before serving.