TO PREPARE THE CUPCAKES: In a small saucepan over medium heat, melt the butter. Cook for several minutes stirring occasionally until the butter turns a golden brown. Pour the butter into a glass bowl to stop it from cooking. Chill the butter until it becomes firm again.
Preheat the oven to 350 degrees F. Place cupcake liners in a muffin pan and set aside.
In a bowl of a stand mixer combine the flour, sugar, baking powder, and cinnamon. Cut up the chilled brown butter, and add it to the dry ingredients. With a paddle attachment, mix on low speed until it has a sandy texture.
Add the oil, sour cream, and milk, and mix until just combined, scraping down the sides as necessary.
In a separate bowl whip the egg whites until medium peaks.
Gently fold the whipped whites into the batter until combined.
Fill the cupcake liners about 3/4 of the way full.
Bake for 15 minutes or until lightly golden and a skewer comes out clean.
Cool before frosting
TO PREPARE THE FROSTING: Brown the butter the same way as it was prepared for the cupcakes. Chill in a glass bowl until it firms up again.
In a stand mixer cream the browned butter, add the powdered sugar and milk and cream until light and fluffy for about 3-5 minutes.
TO PREPARE THE APPLE FILLING: Peel and cut the apples into 1/2 inch cubes.
In a small saucepan over low heat, cook the apples with the sugar and vanilla extract until the apples are tender for 5-8 minutes. Set aside to cool.
To assemble the cupcakes, scoop a small amount of the center out and fill with about a tablespoon of the apple filing. Frost as desired and sprinkle with cinnamon. Enjoy!