01 -
Butter three 20 cm round baking pans, line the bases with parchment paper, butter again, and lightly dust with flour. Set aside.
02 -
Preheat oven to 177°C.
03 -
In a medium bowl, whisk together sifted cake flour, baking powder, baking soda, and salt. Set aside.
04 -
Using a stand mixer fitted with the paddle attachment, cream butter and granulated sugar on medium-high speed until light and fluffy, about 5 minutes. Scrape sides of the bowl as needed.
05 -
Beat in eggs one at a time, then add the egg whites. Mix until incorporated, then blend in sour cream, vanilla extract, and coconut extract until smooth. The mixture may appear curdled.
06 -
Reduce mixer speed to low. Alternate additions of the flour mixture and buttermilk, beginning and ending with the dry ingredients. Mix gently until just combined, avoiding overmixing. Scrape the bowl as required.
07 -
Using a spatula, fold sweetened shredded coconut into the batter until distributed.
08 -
Divide batter evenly among prepared pans and bake for 35 to 45 minutes, or until a tester inserted in the centre comes out clean. Cool cakes in pans on a wire rack for 10–15 minutes, then turn onto racks to cool completely.
09 -
Wipe the mixing bowl and whisk attachment with vinegar or lemon juice to ensure both are free from grease.
10 -
Place egg whites, sugar, and salt in the stand mixer bowl. Set over a saucepan of simmering water and whisk constantly until hot to touch and sugar is dissolved, about 3 minutes.
11 -
Remove bowl from heat, dry bottom, and attach to the stand mixer. Whisk on medium-high speed until mixture is cool and stiff peaks form, 10 to 15 minutes.
12 -
Switch to the paddle attachment. With mixer on medium, add room temperature butter one tablespoon at a time, letting each addition fully incorporate. Continue mixing until smooth, even if buttercream looks curdled or loose.
13 -
Scrape down the mixer bowl, add coconut milk powder, and whip on high until the buttercream is light and thick, about 5 minutes.