Combine egg yolks, milk, vanilla extract, flour, sugar, baking powder, and salt in the bowl of a stand mixer fitted with the paddle attachment. Add butter gradually while mixing on a low speed.
Then add milk and increase speed. Beat for thirty seconds.
The batter is ready. Now transfer the batter to the cake pans.
Bake the cake in the oven for twenty-five minutes. Once baked, place on the wire rack.
Take a bowl to prepare coconut filling. Add coconut custard and cream in a bowl. Mix well until soft peaks form.
In a bowl of a stand mixer, combine sugar and butter and mix well. Now add coconut filling to it and beat for three minutes. Coconut buttercream is ready.
Assemble the cake by slicing them into two layers. Apply buttercream on each layer and top each layer on each other. Spread buttercream on the top and the sides.