Mix the cake mix, sour cream, eggs, sugar & oil.
In separate bowl stir together the brown sugar & cinnamon.
Pour 1/2 of the cake mixture into 9×13 pan. Then add the brown sugar cinnamon mixture.
Pour remaining cake batter on top.
Bake at 275 for 50 - 60 minutes.
While cake is baking, mix the icing ingredients all up together and pour over cake after it's cooled slightly.