Preheat the oven to 350°F (177ºC) and line a cupcake pan with 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 with a hand mixer and large bowl), beat the butter on high until creamy, 2 min. Add the sugar and beat on medium-high until light and fluffy, about 2 min. Turn the mixer to low and add the egg whites one at a time. Mix until well combined. Add 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. 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.
