Preheat your oven to 350°F (180°C). Line the bottom of your baking pan with parchment paper and grease the sides.

Sift the cake flour to ensure there are no lumps.

In a heatproof bowl, combine the white chocolate and butter. Microwave at 15-second intervals, stirring in between, until melted. Alternatively, use a double boiler over medium heat.

Pour heavy cream into another heatproof bowl and microwave for 30-45 seconds until warm.

Add the matcha powder to the melted chocolate-butter mixture and whisk until smooth.

Pour in the warm cream and whisk again until combined. Add in the sifted cake flour and optional salt, whisking until smooth.

Carefully separate the egg yolks and whites into two separate bowls.

Add 50 g of sugar to the egg yolks and whisk until pale yellow. Pour this into the matcha mixture and whisk until smooth.

Using an electric mixer, beat the egg whites on medium speed for about 15-20 seconds. Add the remaining 40 g of sugar and continue whipping on high speed until medium peaks form.

Add one-third of the whipped egg whites to the matcha mixture and combine gently.

Repeat with the next one-third and finally fold in the remaining egg whites until just combined.

Pour the batter into the prepared baking pan. Bake for 20 minutes at 350°F (180°C). Lower the temperature to 325°F (170°C) and bake for another 20-22 minutes until lightly browned.

Alternatively, bake at 320°F (160°C) for 40-50 minutes for a softer top.

Let the cake cool completely in the pan. Once cool, wrap in plastic and refrigerate for several hours, ideally overnight.

Slice with a warm knife and serve as is or topped with whipped cream.