Position oven rack in the center (or just below center) of the oven. Preheat oven to 350°F (175°C). Grease and flour three 8-inch round cake pans. HINT: Line the bottom of the pans with parchment rounds for easy release and clean-up.
Measure sifted cake flour, baking powder, and salt. Sift together three times and set aside.
Whisk together sour cream and coconut milk in a small bowl and set aside.
Using an electric mixer with a large mixing bowl, cream butter and 1 cup of sugar together until light and fluffy. Add coconut extract and mix to combine. Add flour mixture alternately with coconut milk and sour cream mixture, beating after each addition. Remove bowl from mixer and set aside.
In a medium mixing bowl, beat egg whites until foamy. Add ½ cup sugar gradually, beating until meringue will hold medium peaks. (Medium peaks can hold their shape, but the peak curls over when the beaters are lifted.)Use a clean spatula to gently fold beaten egg whites into batter. (Do this step by hand. Do not use a mixer.)
Pour the batter evenly into the three prepared cake pans. Bake layers in a preheated oven for 25-30 minutes (8" pans) or until a toothpick or skewer comes out clean. Always test the cake before taking it out of the oven. Allow cakes to cool in their pans over a wire rack for 10 minutes. Carefully tap out onto wire rack to cool completely. Wrap layers in plastic and chill in refrigerator for at least an hour.
Frosting
Using an electric mixer, beat butter on medium-high until light and fluffy. Add coconut and vanilla extracts and salt and mix to thoroughly combine. Slowly add powdered sugar, mixing well after each addition.
Add coconut milk, one tablespoon at a time time, beating on medium-high until fully incorporated.
Once the cake is completely chilled, trim the layers. Spread the top of the bottom layer of cake with frosting. Add the middle layer and frost top. Add the top layer. Apply a crumb coat to the entire cake. (A crumb coat is a thin layer of frosting that covers the top and sides of a cake.) Return the cake to the refrigerator for 10-15 minutes.
Frost the entire cake with a generous layer of frosting. Sprinkle flaked coconut over top and sides of cake before the frosting sets.
Notes
The time/temp in this recipe was set using 3 parchment-lined 8" stainless steel round cake pans.If you use glass or dark pans, or pour only two layers instead of three, you may need to adjust the baking time and/or temperature.Glass cake pans: When baking cake layers in glass pans, lower the baking temperature to 335°F (168°C), and bake 8-10 minutes longer, depending on your oven.Dark cake pans: Drop the baking temperature to 335°F (168°C) and bake 6-10 minutes longer, depending on your oven.9-inch pans: Drop the baking temperature to 335°F (168°C) and bake for about 22-25 minutes, depending on your oven.How to know if your cake is done:
The edges of the cake pull away from the sides of the pan.
The cake springs back when gently pressed.
When inserted near the center, a toothpick comes out clean.
The internal temperature, measured on an instant-read thermometer, is 210°F (99°C).