Preheat your oven to 340°F (170°C). Line an 8-inch round cake pan with parchment paper. In a large bowl, beat the eggs and sugar together using a stand mixer or hand mixer until the mixture becomes pale, thick, and tripled in volume—this should take about 8-10 minutes. The ribbon stage is achieved when the batter falls from the beaters in thick ribbons that hold their shape for a few seconds.

Sift the cake flour over the egg mixture in three batches, gently folding with a spatula after each addition. Be careful not to deflate the batter. Add the melted butter and vanilla extract, folding gently until just combined. Pour the batter into the prepared pan and bake for 25-30 minutes, or until golden brown and a toothpick inserted comes out clean.

Allow the cake to cool completely on a wire rack. Meanwhile, slice about two-thirds of the strawberries and toss them with 2 tablespoons of sugar to macerate. Whip the heavy cream with powdered sugar and vanilla until stiff peaks form. Reserve some whole strawberries for decoration.

Slice the cooled sponge cake horizontally into two even layers. Place the bottom layer on a serving plate and spread with a generous layer of whipped cream. Arrange the macerated strawberry slices over the cream. Top with the second cake layer. Cover the entire cake with whipped cream, smoothing the sides and top. Decorate with reserved whole strawberries and dust with powdered sugar.

Refrigerate the cake for at least 2 hours before serving to allow the flavors to meld and the cream to set. This resting period is crucial for achieving the perfect texture that makes this fluffy Japanese dessert so distinctive.