Preheat the oven to 350°F (177ºC) and line a cupcake pan or muffin tin with standard cupcake liners.

Whisk together the sifted cake flour, baking powder, baking soda, and salt. Set aside.⁣

In the bowl of your stand mixer fitted with the paddle attachment (or using a hand mixer with a large bowl), beat the butter on high for 2 minutes until light and creamy. Add in the sugar and beat on medium-high until light and fluffy, about 2 minutes. Scrape down the bowl and paddle as needed. Turn the mixer to low and add the egg whites one at a time. Mix until well combined. Add in the vanilla, coconut extract, and sour cream, then mix for 1 minute on high.⁣

Add the dry ingredients all at once and mix on low until just combined, then continue mixing while you add the canned coconut milk in a slow, steady stream. Mix until smooth, then gently fold in the shredded coconut with a rubber spatula.⁣

Pour the batter evenly into the prepared cupcake tins and bake for 15-18 minutes, or until a toothpick inserted comes out clean.⁣

With a hand mixer or paddle attachment on your stand mixer, beat the butter on medium-high until it’s creamy and light (almost white) in color, about 7 minutes. Scrape down the bowl and paddle and add the powdered sugar about a cup at a time and mix on low speed until fully incorporated. ⁣

Add the coconut extract, vanilla, milk, and a pinch of salt. Continue mixing on low speed until fully incorporated and smooth.⁣

When the cupcakes are fully cooled, prepare a piping bag with Wilton Tip 1A (or snip off ½ inch opening) and fill it with coconut buttercream. Add the shredded coconut topping into a small bowl, if using. Pipe a swirl onto each cupcake, then gently dip the frosted cupcake into the shredded coconut.