Preheat the oven to 350°F (176°C). Line the bottom of 3 (8-inch [20-cm]) cake pans with parchment paper and grease the sides.
In a large mixer bowl, cream the butter and sugar together on medium speed until light in color and fluffy, 3 to 4 minutes. Add the sour cream and vanilla extract and mix until combined.
Add 3 of the egg whites and mix until well combined. Add the remaining 3 egg whites and mix until well combined. Scrape down the sides of the bowl as needed to make sure everything is combined.
Combine the flour, baking powder, cinnamon and salt in a medium bowl. Combine the milk and water in a small measuring cup. Add half of the flour mixture to the batter and mix until combined. Add the milk mixture to the batter and mix until combined. Add the remaining half of the flour mixture and mix until smooth. Scrape down the sides of the bowl as needed to ensure everything is well combined.
Divide the batter evenly between the prepared cake pans. Bake the cakes for 23 to minutes, or until a toothpick inserted in the middle comes out with a few crumbs. Remove the cakes from the oven and allow them to cool for 2 to 3 minutes, then remove them from the pans and transfer them to a cooling rack to finish cooling.