Preheat oven to 325 degrees F. Prepare three 8 inch or four 6 inch round pans with nonstick spray, parchment paper and another layer of nonstick spray.

Sift together flour, baking powder, salt and cinnamon. Set aside.

Stir vanilla into buttermilk. Set aside.

In the bowl of a stand mixer, beat the butter and sugar on medium-high speed using the paddle attachment. Cream until pale and fluffy, about 5 minutes.

With the mixer on low, add egg whites one at a time. Mixing well after each egg.

Add one third of your dry ingredients and mix just until combined. 

Add one half of your buttermilk. Mix. Alternate ingredients again. Dry, wet, dry and mix gently. Do not over mix.

Divide batter evenly between the prepared pans. Bake 35-40 minutes. Cake is finished when a toothpick comes out with a few moist crumbs on it. 

Cool 10-20 minutes before inverting cakes from pans. Cool completely before assembling cake or wrap with plastic wrap and refrigerate if not using until the next day.

Combine all the ingredients in a bowl and stir until incorporated.

In a small sauce pan, heat the cream to a simmer and then pour over the white chocolate chips in a separate bowl. 

Let the cream sit on top of the chips for 10 minutes, and then stir until glossy and shiny. 

In a stand mixer, fitted with the paddle attachment, cream the butter and brown sugar together for 3-6 minutes until nice and fluffy.

Gradually add the powdered sugar, and then the vanilla, cinnamon and salt. Beat until fluffy, about 5 minutes. You can add a tablespoon or two of cream if the frosting feels too dense. Beat the frosting again for another few minutes.

Frost the cake with the remaining brown sugar buttercream. Can be stored in the refrigerator, covered, overnight but make sure to serve room temperature.