Preheat oven to 325 degrees.
1 box yellow cake mix
4 eggs (I have used 3 eggs and you can't tell the difference)
3/4 cup vegetable oil
8 oz sour cream
1 cup brown sugar
1 tbsp cinnamon
2 cups confectioner's sugar
4 Tbsp milk
1 tsp vanilla
Mix the first four ingredients by hand. Spread half of the batter in a greased and floured 9x13 pan. you can just use cooking spray if you like.
Mix brown sugar and cinnamon in a seperate bowl. Sprinkle over the batter in the pan.
Top with the remaining batter, easiest by spooning it on. It does not have to completely cover the brown sugar mixture.
Bake for about 40 minutes.
Mix the powdwered sugar with the milk and vanilla, you may need a little more milk to get the consistency right.
Poke holes in the hot cake with a fork and pour icing on top while still hot.