Preheat a convection oven to 170°C (340°F) and line an 18cm round cake pan with parchment paper.

Sift the cake flour and 10g of matcha powder together three times to ensure uniform aeration and particle distribution.

Combine eggs and granulated sugar in a stand mixer bowl and whisk over a bain-marie until the mixture reaches 40°C (104°F).

Beat the egg mixture on high speed until it reaches the ribbon stage, characterized by a thick, pale foam that holds its shape for 3 seconds.

Gently fold the sifted dry ingredients into the egg foam in three batches using a spatula, maintaining as much volume as possible.

In a separate small bowl, combine the melted butter, milk, and vanilla extract; temper with a small amount of batter before folding the mixture into the main batter.

Pour the batter into the prepared pan from a height of 20cm to pop large air bubbles and bake for 25 minutes.

Invert the cake onto a wire rack immediately after removal from the oven to prevent the structure from collapsing while cooling.

Prepare the frosting by whipping heavy cream, confectioners sugar, and 5g of matcha powder to stiff peaks.

Slice the cooled sponge horizontally into two even discs, apply a layer of matcha cream between them, and frost the exterior surface.