• Preheat the oven to 170°C (338°F). Line the sides and base of a deep 6" x 3" (15 x 7.6 cm) or regular 7" (18 cm) round pan with parchment paper.
• To set up a stovetop bain-marie (double boiler), heat a medium-sized pot filled with an inch of water until barely simmering. Turn off the heat.

Make the matcha sponge cake

• Sift cake flour, baking powder, salt, and matcha powder into a mixing bowl.
• In a heatproof mixing bowl, lightly beat eggs and sugar to combine. Place the bowl over the bain-marie, and keep beating with a whisk until the mixture warms to between 33 - 36°C (91.4 - 96.8°F). Immediately pour the egg mixture into the bowl of a stand mixer (or whip directly in the bowl with handheld beaters).
• Whip on medium-high speed until the egg mixture greatly increases in volume, turns pale and foamy and reaches the ribbon stage ^{Note 3}, about 8 to 10 minutes.
• Reduce mixer speed to low and whip for another 1 – 2 minutes until the mixture looks very smooth and glossy (gets rid of big air bubbles in the batter).
• Sift the flour-matcha mixture over the egg batter in 3 additions, each time folding in gently (don't lose those trapped air bubbles) with a rubber spatula until well incorporated.
• Next, gently fold in the milk until well incorporated. Lastly, gently fold in the oil until the batter is of the same consistency throughout. Once the batter runs smoothly off the spatula without breaking or clumping, it is at the ideal consistency.
• Bring the mixing bowl as close as you can to the cake pan and pour gently to prevent the batter from deflating. Run a bamboo or metal skewer through the batter. Tap the pan twice firmly on the counter. Bake in the preheated oven for 40 minutes until the top of the cake turns brown. 

  Test for doneness: Gently press a few fingers on the top of the cake - it should spring back when done. If your fingers leave impressions, the cake isn't quite done yet. Bake for another 5 minutes before checking again.
• Remove the pan from the oven and immediately drop it onto the counter from a height of 6" (15 cm) - this minimizes shrinkage. Let the cake sit in the pan for 5 minutes. Release the cake, and peel away the baking paper from the sides and bottom. Cool on a wire rack.

Make the mascarpone whipped cream

• In a stand mixer fitted with a whisk or using handheld beaters, beat cold mascarpone cheese on medium speed for about 15 seconds. Slowly pour in roughly ½ of the cold whipping cream, allowing the mixture to combine and become more liquid.
• Add the remaining cold whipping cream and continue whipping until the whisk starts to leave faint tracks in the cream. Add the icing sugar and vanilla extract and reduce speed to low.
• At this point, watch closely (I like to finish up by hand) and stop once the mixture is thick, firm and forms stiff peaks. Caution: This can happen quickly - be careful not to over-beat or else you'll end up with a curdled, clumpy mess. Chill until needed.

Make the stabilized matcha whipped cream

• In a small bowl, sprinkle gelatin powder over cold water and let it sit for 5 minutes. Microwave on a low-medium power setting for 10 - 15 seconds until the gelatin is fully dissolved. Set aside to cool to room temperature.
• In a clean (preferably chilled) mixer bowl, combine cold whipping cream, icing sugar, matcha powder, and vanilla bean paste or extract. Whip on medium-high speed until the mixture starts to thicken (again, watch for the whisk leaving tracks in the cream) and forms soft peaks.

  Note: I recommend tasting the cream at this point. Add more matcha powder if you prefer a bolder flavour or deeper hue.
• Pour in the room-temperature gelatin mixture all at once. Continue whipping until stiff peaks form.

Assemble the cake

• Slice the cooled matcha sponge cake into 3 layers. Reserve ¼ cup of mascarpone cream for a crumb coat.
• Place one of the cake layers on a serving plate. Spread a thin layer of mascarpone cream with an offset spatula. Scatter ½ of the canned azuki beans on top (leaving 0.5"/1 cm of the edges free), and cover with another thin layer of mascarpone cream.
• Place another cake layer on top and spread the mascarpone cream and remaining azuki beans. Put the final cake layer on top. Fill any gaps in the sides of the cake with the reserved mascarpone cream. Use any left-over cream for a crumb coat. Chill the cake for 15 minutes to allow the mascarpone cream to firm up a bit.

Cover and decorate the cake

• Spread a thick layer of matcha whipped cream around the sides and across the top of the cake. Smoothen with a metal scraper or offset spatula.
• Fit a piping bag with your favourite piping tip. Fill with left-over matcha whipped cream and pipe your desired decorations on the top and/or around the base.
• Top with red azuki beans (if you have extra), choice of berries, fresh mint leaves and edible flowers. Chill for at least an hour before serving.