Mix cake mix, oil, eggs, and sour cream by hand, about 50 strokes.

Put half the batter in 9x13 pan.

Combine brown sugar and cinnamon and spread over entire cake. Spread the rest of the batter on top of this. Use knife to make swirls in the cake.

Bake at 325° for about 40 minutes. Blend powdered sugar, milk and vanilla and spread on warm cake.