- Preheat the oven to 350 degrees F, grease and flour a bundt pan. We used a bundt pan with a 12 cup baking capacity, 10 inches across. See notes re: pan size 
- In a medium sized bowl add the cake flour, baking powder, baking soda and salt. Whisk to blend, set aside. 
- In another bowl or measuring cup add the sour cream, milk, vegetable oil, and vanilla extract. Blend with a fork and set aside 
- In the bowl of your mixer, mix the softened butter until smooth. Gradually add the sugar and mix on medium speed for 3 to 5 minutes until it is lightened in color and fluffy. 
- Add the eggs one at a time, mixing after each until the yellow of the yolk has blended. 
- With the mixer on low speed, add the flour mixture and the sour cream mixture alternately, beginning and ending with the flour mixture (We did 3 additions of dry ingredients and 2 of wet). Mix just until combined. 
- Add 3.5 cups(about half) of the cake batter to the prepared bundt pan. 
- Then, sprinkle the cinnamon and brown sugar mixture over the batter. We recommend not carrying the mixture all the way to the edge of the pan or to the center tube/core of the pan. (We explain this in the notes.) 
- Top with the remaining cake batter and gently smooth with the back of a spoon. Tap the filled cake pan on your counter a few times to make the air bubbles rise. 
- Bake at 350 degrees for 45-50 minutes and then check for doneness-it may need additional time. Bake until a toothpick inserted into the center comes out clean or with just a few crumbs attached. Allow the cake to cool in the pan, on a wire rack for 10 minutes before turning out.    
- Makes 7 cups of cake batter