Sift 1 tbsp matcha powder into a bowl and add 150 ml hot water. Whisk until incorporated and then add 2 tbsp granulated sugar. Whisk thoroughly until the sugar has dissolved.
Transfer to a container tall enough to submerge the ladyfingers. Add another 150 ml water, this time at room temperature. This will cool the mixture quickly. Set aside for later.
Pour 100 g granulated sugar and 120 ml water into a saucepan. Heat on medium and mix to help dissolve the sugar. Once dissolved, stop stirring and allow it to bubble until it reaches 120 °C (248 °F). (Tip: the syrup will thicken and bubbling will slow down around the correct temperature, but check regularly with a thermometer to ensure accuracy.)
Add 4 egg yolks to a large heatproof bowl (I used a glass mixing bowl). Once the sugar has reached 120 °C (248 °F), take it off the heat and start whipping the egg yolks on high with an electric mixer. Slowly pour in the syrup while whisking.
Once all of the syrup is added, reduce the speed to medium-high and continue to whip until the egg yolks are pale, smooth and thick enough to draw ribbons.
Place 400 g mascarpone cheese in a separate mixing bowl and mix to soften. Sift in 2 tbsp matcha powder and roughly mix it in. Add 200 ml heavy cream and then whip with an electric mixer on medium-high speed until it's firm enough to form peaks.
Pour the egg mixture into the matcha mascarpone cream and fold until combined.
Take your 8" square cake pan or a deep baking dish with similar dimensions. Dip the ladyfingers in the matcha for about 1-2 seconds at a time and arrange in one layer at the bottom of the container. Use a sifter to sprinkle the top with matcha powder before adding half of the matcha cream mixture.
Repeat another layer of matcha-dipped biscuits and cream. Smooth the top with a spatula and then chill in the refrigerator for at least 4-6 hours (overnight is recommended).
Sprinkle the top with matcha powder right before serving and enjoy!