In a small bowl, combine 1 cup of the sugar and 2 teaspoons of cinnamon; set aside.
Preheat the oven to 325 degrees F. Using a spray product like 'Pam with Flour' to generously spray a 9-inch bundt cake pan, being careful to cover all the nooks and crannies, as well as the center tube. (Note: If you don't want to use Pam with Flour, you can just rub the pan with shortening.) Gently dust the entire inside of the pan with the sugar and cinnamon mixture. You should only need about ¼ to ½ cup of sugar, but you want to try and evenly coat the inside surface of the pan, including the tube. Save the remaining sugar and cinnamon mixture and set everything aside.
Sift together the flour, baking powder, baking soda and salt; set aside.
In a large bowl, use an electric mixer to beat the butter on medium speed for one full minute. Add the white sugar and mix for 3 minutes, until light and fluffy. Scrape down the bowl and blade and add the brown sugar. Mix for 2 minutes until the mixture looks light brown and uniform in color. Add the eggs one at a time, beating each for 1 full minute. Stir in the vanilla. Add the flour mixture alternately with the sour cream; beat well.
Spread half of the batter into the prepared pan. Sprinkle with ¼ to ⅓ cup of the remaining cinnamon sugar mixture over the top of the batter. If you're using cinnamon chips, sprinkle those in there too. Spread the rest of the batter into the pan and sprinkle any remaining sugar mixture over the top.
Bake in the preheated oven for 55 to 65 minutes, or until a toothpick inserted into the cake comes out clean. Allow to cool for 10 minutes before inverting onto a wire rack to cool completely.
ADD THE ICING:
Use a large spatula or flat cookie sheet to slide under the cake and move it to a platter. Use an electric mixer to blend together the icing ingredients in a large bowl. Add just enough milk to make the icing thin enough so that it will drip down the sides of the cake, but not so thin that it will drip off of the cake. If you accidentally get it too thin, just add more powdered sugar. Spoon the icing onto the top of the cake and let it ooze down the sides. Refrigerate until ready to serve.
Notes
Nutritional information does not include the optional cinnamon chips.