Preheat oven to 325 degrees F. Prepare a 12-cup bundt cake with nonstick spray and a dusting of sugar. Set aside.
Whisk together the flour, baking powder, salt and cinnamon. Set aside.
In the bowl of an electric mixer, beat the butter and sugar on medium-high speed using the paddle attachment for 3 to 5 minutes, until light and fluffy.
With the mixer on low, add egg whites one at a time. Mixing well after each egg white. Stir in the vanilla and then beat the mixture until smooth, about 2 to 3 more minutes.
With the mixer on low, alternately add the dry ingredients and the buttermilk, starting and ending with the flour mixture. Stir until combined.
Pour half of the batter into the bundt pan. Evenly sprinkle the cinnamon sugar mixture over the batter. Pour the remaining batter on top of the cinnamon sugar mixture. Bake about 50 to 60 minutes. Cake is finished when a toothpick comes out with a few moist crumbs on it.
Cool the cake in the bundt pan until it's completely cooled. Invert onto a cake stand.