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, 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 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 flour mixture (3 additions of dry ingredients and 2 of wet). Mix just until combined.
Gently fold the blueberries into the cake batter. (The batter is thick).
Add HALF of the cake batter to the prepared bundt pan.
Then, sprinkle the cinnamon mixture evenly on top of it.
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 or 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. Check at about 40 minutes, if the top of the cake is becoming too dark, cover loosely with aluminum foil.
Makes 7 cups of cake batter