Matcha Tiramisu

Preheat oven to 210°C (conventional) / 200°C (convectional). Draw two 20-cm circles on a piece of parchment paper. Flip the parchment paper (drawing side down) and place on a baking sheet.
Sift plain flour and potato starch together in a separate bowl. Set aside.
40 grams plain flour, 20 grams cornstarch
Using an electric mixer, whisk egg white and caster sugar on high speed until almost-stiff peaks.
60 grams egg whites, 60 grams caster sugar
In a separate bowl, use the electric mixer to whisk the egg yolk until thick and pale (no need to wash the beaters).
40 grams egg yolks
Fold egg whites into egg yolks. Add in flour mixture and fold until just incorporated, taking care not to deflate the precious air bubbles whipped into the egg.
Transfer batter into a piping bag fitted with a plain round nozzle. Pipe two 20-cm rounds on the parchment paper, maintaining an even height of around 0.5cm throughout. Use an offset spatula to spread the batter if needed. Bang the baking sheet twice to get rid of excess air bubbles. Dust with icing sugar.
Icing sugar
Bake for 7 minutes. Open the oven to release the steam, then close and bake for another 2 minutes until savoiardi are lightly golden.
Let savoiardi cool completely. Slide a clean offset spatula to separate them from the parchment paper.
If the savoiardi spread bigger than 20cm, use a cake ring and cut them into 20cm rounds. Set aside till Assembly Part 2.

Place berries and sugar in a pot. Bring to a simmer and mash the berries into small pieces (note: small enough so that you can pipe the compote later on).
150 grams berries, 30 grams caster sugar
Simmer for 5 minutes until slightly thickened - able to draw a line through the compote and the line stays separate briefly.
Let cool completely, transfer mixture into a piping bag.

Sift matcha into a bowl. Pour in hot water in four parts, whisking after each addition until the matcha is smooth and incorporated. Set aside until assembly.
10 grams matcha, 120 grams hot water

For whipping cream: place a metal bowl and beaters into the fridge.
Separately, place egg yolks in a heatproof bowl. Add in Part A sugar and whisk immediately until sugar is incorporated. Whisk in Grand Marnier.
60 grams egg yolks, 30 grams caster sugar, 30 grams Grand Marnier
Place the bowl over a pot of barely simmering hot water (the water should not be touching the base of the bowl). Whisk constantly until the mixture reaches 60°C. Turn off the heat and continue whisking for 3 minutes. The zabaglione will thicken and become light and pale.
Remove bowl from heat and continue stirring until zabaglione has cooled to room temperature. Whisk in mascarpone gently until incorporated. Set aside.
250 grams mascarpone
Pour cream into the chilled metal bowl. Add in Part B sugar and sifted matcha. Beat with an electric mixer until soft peaks. The cream stiffens fast so watch it - do not overbeat.
250 grams cream, 35 grams caster sugar, 10 grams matcha
Fold ⅓ of the cream into the mascarpone mixture to lighten it. Pour the lightened mascarpone mixture into the remaining whipped cream and fold until incorporated.
Use immediately for Assembly Part 2.

Place one of the savoiardi into the cake ring. Whisk the Matcha Syrup (in case the matcha has settled to the bottom) and brush ⅓ of the Matcha Syrup on the savoiardi.
Spread Matcha Mascarpone until it comes up to halfway of the cake ring. Pipe Berry Compote evenly on the Matcha Mascarpone. Lift up the cake and tap it gently a few times on the countertop to allow the mascarpone to fill out any gaps and remove large air bubbles.
Whisk the Matcha Syrup again and brush ⅓ of the Matcha Syrup on the other savoiardi. Place savoiardi syrup side down into the cake ring. Brush remaining Matcha Syrup on the savoiardi.
Spread Matcha Mascarpone until it reaches the top of the cake ring. Use a large spatula to smooth the surface.
Refrigerate the tiramisu overnight.
Chill remaining Matcha Mascarpone in a piping bag.

Remove the cake ring. Pipe patterns with remaining Matcha Mascarpone if desired. Dust with additional matcha powder and serve immediately.
Additional matcha
Tiramisu should be served immediately cold from the fridge. If possible, the matcha powder should be dusted just before serving to prevent it from absorbing moisture. Remove the acetate strip just before cutting and slicing, or scoop and serve.