Mix together the cake mix, sugar, eggs, oil,
and sour cream. Separately mix 1 cup
brown sugar with the 5 tablespoons cinnamon.
Pour 1/2 of the cake batter into a greased 9 x 12
pan. Sprinkle half of the brown sugar mixture over
the batter and swirl it together with a knife.
Pour remaining batter in as well as the other
half of the brown sugar mixture. Swirl again.
Bake at 325 degrees for 45 minutes.
Mix frosting ingredients and beat until smooth.
Pour over hot cake.