Pre-heat the oven to 350 and line each well of a 12 well cupcake tin with a paper liner. Whisk the flour, baking powder and cinnamon together in a bowl and set it aside. Then set up a stand mixer and combine the butter, sugar and mascarpone in its bowl. Beat them together thoroughly with the paddle attachment until fluffy. Then add the vanilla, followed by the egg whites. Finally, alternate adding 1/3 of the dry ingredients followed by 1/2 of the buttermilk. Repeat, then finish the batter with the last 1/3 of the dry ingredients. Fill the paper liners just over halfway with the batter and bake the cupcakes for 15-20 minutes. A toothpick should come out cleanly. Let them cool for a couple of minutes in the tin, then remove them to a rack to finish cooling completely.