Step 1

Preheat the oven to 325°F. Coat a 9×13 pan with nonstick spray and set aside.

Step 2

In the bowl of your stand mixer combine the cake mix, eggs, oil, vanilla and sour cream. Mix on low for 30 seconds and then raise the speed to medium and mix for 2 minutes, scraping the sides of the bowl as necessary.

Step 3

Spread the cake batter into your prepared pan. In a medium bowl whisk together the brown sugar and cinnamon. Sprinkle this evenly on top of your cake.

Step 4

Using a butter knife gently swirl the cinnamon sugar into the cake batter. Don’t over-swirl, as you want ribbons of the mixture throughout the cake.

Step 5

Bake for 35-40 minutes or until a toothpick entered into the center of the cake comes out clean.

Step 6

Cool cake for 15-20 minutes.

Step 7

In a medium bowl whisk together the powdered sugar and milk. Pour this over the slightly warm cake. Allow the icing to set, or eat right away!