"I just love the combination of plum liqueur and green tea. Similar recipes make use of either sake or orange liqueur, but my experiment with Choya® was a good one. Before serving, dust with matcha or confectioners' sugar."
Bring water and 1/4 cup sugar in a saucepan to a boil. Remove from heat and stir in 2 tablespoons matcha. Add 1/2 cup plum liqueur. Let matcha syrup steep and cool.
Fill another saucepan halfway with water and bring to a boil. Reduce heat to bring water down to a simmer.
Place egg yolks and 2/3 cup sugar in a large bowl. Set bowl over simmering water and whisk constantly until the mixture is pale yellow and thick ribbons fall from the whisk, 4 to 5 minutes. Remove from heat and fold in mascarpone cheese until smooth and creamy. Mix in 2 1/4 teaspoons matcha.
Whip heavy cream in a chilled glass or metal bowl with an electric mixer until stiff peaks form. Whisk in 2 tablespoons plum liqueur and vanilla extract. Fold in mascarpone mixture until blended and smooth.
Beat egg whites in a clean glass, metal, or ceramic bowl until stiff, sharp peaks form. Fold 1/3 of the egg whites into the mascarpone cream. Repeat twice more, folding gently until egg whites are incorporated.
Dip ladyfingers in matcha syrup one at a time until just soaked. Arrange a layer of ladyfingers on the bottom of a 6-quart container. Spread 1/2 of the mascarpone cream on top. Repeat with remaining soaked ladyfingers and mascarpone cream.
Cover tiramisu with plastic wrap and refrigerate until flavors combine, at least 4 hours.