Start out by preheating the oven to 250 degrees and preparing a 9x13 baking pan with nonstick spray.

In a large mixing bowl or using your stand mixer combine the cake mix, oil and sour cream. Mix until combined. Starting out on a low speed and slowly speeding up.

Spread the 1/2 of the batter into your prepared pan.

In a small mixing bowl combine brown sugar and cinnamon. Mix thoroughly.

Sprinkle the brown sugar mixture of the batter in the prepared pan.

Bake for about 30 minutes or until golden brown and toothpick done.

In a small bowl, combine powder sugar, milk, and vanilla. Mix completely. You can add more or less milk to get desired consistency.

Poke a few small holes in the cake and ice your cake.

Allow cake to sit and cool for a bit. The icing should slightly harden, and enjoy.