Make the Cinnamon Cake:

1. Prepare three 8 inch cake pans with parchment paper circles in the bottom and grease the sides. Preheat oven to 350°F (176°C).
2. In a large mixing bowl, cream butter and sugar together until light in color and fluffy, about 3-4 minutes. Do not skimp on the creaming time.
3. Add sour cream and vanilla extract and mix until well combined.
4. Add egg whites in two batches, mixing until well combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
5. Combine dry ingredients in a separate bowl, then combine the milk and water in a small measuring cup.
6. Add half of the dry ingredients to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
7. Divide the batter evenly between the cakes pans and bake for about 23-25 minutes, or until a toothpick comes out with a few crumbs.
8. Remove the cakes from the oven and allow to cool for about 2-3 minutes, then remove to cooling racks to cool completely.

Make the Cinnamon Frosting:

1. Beat the butter and shortening together until smooth.
2. Slowly add half of the powdered sugar and mix until smooth.
3. Add the vanilla extract, ground cinnamon and water or milk and mix until smooth.
4. Slowly add remaining powdered sugar and mix until smooth. Set aside.

Make the Cinnamon Sugar Glaze:

1. Add the powdered sugar, brown sugar and cinnamon to a small bowl and whisk to combine. Add the water and whisk until smooth.

Assemble the Cake:

1. To put the cake together, use a large serrated knife to remove the domes from the top of the cakes so that they’re flat. Place the first cake on a serving plate or a cardboard cake round.
2. Spread 2 1/2 tablespoons of cinnamon sugar glaze over the cake layer. Allow it to soak into the cake. Spread 1 cup of frosting in an even layer on top of the cake.
3. Repeat the process with the second layer of cake, glaze and frosting, then add the final layer of cake on top. Set cake aside.
4. Divide the remaining frosting into 3 bowls, with an extra 1 ½ to 2 cups of frosting in one bowl. Leave the bowl with the larger amount of frosting as is, and color the other two bowls with gel icing color to get two other shades of brown.
5. Spread the darkest shade of frosting into an even layer around the bottom of the cake. Add the other colored frosting to the middle of the cake. Finish the top of the cake with the regular uncolored frosting. Smooth out the sides of the cake.
6. To finish off the cake, pipe swirls of frosting around the top edge using an open star tip. I combined the remaining frosting (all shades) and allowed the colors to swirl together.