Coffee Cake

1 pkg. Duncan Hines yellow cake mix
1/2 c. cooking oil
1 8-oz. carton sour cream
4 eggs
Vanilla [to taste?]

Mix all ingredients except eggs, then add eggs one at a time. Beat 7 minutes. Pour half of batter into greased and floured tube pan. Sprinkle heavily with cinnamon and sugar mixed half-and-half. Cut with spatula. Pour in other half of batter and repeat with cinnamon and sugar. Cut in. Bake at 300° for 1 hr. 1 min.