Mix cake mi, oil, eggs and sour cream by hand, about 50 strokes.
Put half the batter in a 9x13" pan.
Combine brown sugar and cinnamon and spread over the entire cake.
Spread the rest of the batter on top. Use a knife to make swirls in the cake.
Bake at 325 degrees F for about 40 minutes.
Blend powdered sugar, milk and vanilla extract and spread on warm cake.