Preheat oven to 350 F. Combine the flour, baking powder, baking soda, salt and spices in a small bowl, and whisk them together. Set aside for a moment.
Place the butter and both sugars in the bowl of a stand mixer fitted with a paddle attachment. Beat on medium speed until light and fluffy, about 3 minutes. Add the eggs one at a time, beating well after each addition, then add the vanilla extract.
Turn the mixer speed to low and add about a third of the dry ingredients. Once the dry ingredients are incorporated, add half of the buttermilk and mix it in. Add half the remaining drys, then the rest of the buttermilk, and finish with the remaining dry ingredients. Stop the mixer when just a few streaks of flour remain. Finish mixing by hand with a rubber spatula, scraping the bottom and sides of the mixing bowl well.
Scoop the batter into 18 cupcake liners. Bake for 20 minutes at 350 F, until the tops spring back lightly when touched. Cool completely.
To Make the Cinnamon Buttercream:
Combine the whites, powdered sugar, and salt in the bowl of a large stand mixer fitted with a paddle attachment. Mix everything together on low speed, until the sugar is moistened and no dry patches remain. Turn off the mixer, scrape down the sides and bottom of the bowl with a spatula, then turn the mixer to medium speed. Beat on medium for 5 minutes.
After 5 minutes, turn the mixer to medium-low and start adding the softened room temperature butter, 1-2 tablespoons at a time. Once all of the butter is incorporated, add the vanilla extract and cinnamon and mix it in. Stop the mixer and scrape down the bottom and sides once more. Turn the speed to medium and beat the buttercream for 10 minutes. At the end, you’ll have a frosting with a wonderfully light and creamy texture. It can be used right away, or stored in the refrigerator for up to two weeks, or the freezer for up to two months. If you have chilled the frosting, let it come to room temperature and then beat it for several minutes to smooth it out and restore its texture before using it.
Fit a piping bag with a large open star tip, and fill it with cinnamon buttercream. Pipe a big dollop of frosting on top of each cupcake, and if desired, add a few gold sprinkles. Finish by gently place a chocolate feather on top of each cupcake.