Preheat the oven to 325ºF. Grease the bottoms of three 9-inch cake pans or line the bottoms of the cake pans with parchment paper. Leave the sides of the cake pans ungreased.
Beat the egg yolks:
Add the egg yolks to a large mixing bowl and beat with an electric mixer until pale and thick; they will increase in volume. This takes about 5 minutes of consistent mixing.
Add the sugar, 2 tablespoons at a time, mixing well after each addition. Add the buttermilk and mix until incorporated.
Sift the flour and baking powder into the egg yolks.
Prepare the egg whites:
Beat the egg whites until stiff peaks form.
Finish the batter:
Fold the egg whites into the batter and stir gently until combined.
Bake the sponge cakes:
Divide the batter between the prepared cake pans. Transfer to the oven for 30 minutes or until the sponge cake is firm to the touch and a toothpick inserted into the center of the cake comes out clean.
Cool the sponge cakes:
Remove the sponge cakes from the oven and let cool for 5 minutes. Use a butter knife or a thin spatula to run around the sides and bottom of the pan to separate the cake from the pan. Flip the pan over onto a wire rack and lightly tap the bottom of the pan to release the cake if needed.
Allow the sponge cakes to cool for at least 1 hour. Once cool, you can wrap them in plastic wrap until you’re ready to begin the cake.
Make the frosting:
Beat the butter until smooth. Add half the sifted powdered sugar and mix until combined, about 2 to 3 minutes. Add the rest of the powdered sugar and continue mixing until smooth, about 3 to 5 minutes. Add the coconut extract, vanilla extract, and heavy cream and continue mixing until a creamy consistency is met. Add more milk or cream if needed.
Assemble the cake:
Place a sponge cake on a cake stand and add two heaping tablespoons of the frosting. Smooth it out and place a second sponge cake on top. Add two heaping tablespoons of frosting. Add the third sponge cake on top. Add two heaping tablespoons of frosting on top and smooth it out with an offset spatula. Sprinkle the top of the cake with toasted coconut flakes.
Use half of the remaining frosting around the sides of the cake, smoothing it out with an offset spatula. Add the rest of the frosting to a piping bag with a star tip. Decorate the top of the cake with puffs of frosting around the top of the cake and the bottom edge of the cake if you like.
Finish the cake with edible flowers if you like.
To serve:
Slice the cake into pieces and enjoy!
Notes
Note 1: If you like, you can use more coconut flakes and spread them all over the exterior of the cake. I prefer coconut flakes only on the top of the cake.