In a large bowl, whisk together egg yolks and 1/4 cup sugar until the mixture is pale and slightly thickened.
In a separate bowl, beat the heavy whipping cream with the remaining 1/4 cup sugar and vanilla extract until it forms stiff peaks.
Gently fold the mascarpone cheese into the whipped cream mixture until well combined, being careful not to deflate the cream. Add the egg yolk mixture into the mascarpone and whipped cream mixture until fully incorporated.
In a shallow dish, whisk warm water with 2 tablespoons of matcha powder until fully dissolved.
Quickly dip each ladyfinger into the matcha mixture, making sure not to soak them, and lay them in a single layer on the bottom of an 8x8 inch serving dish.
Spread half of the mascarpone cream over the layer of ladyfingers.
Add another layer of matcha-dipped ladyfingers on top of the cream.
Top with the remaining mascarpone cream, smoothing out the top with a spatula.
Sift additional matcha powder over the top for a vibrant finish.
Cover and refrigerate the tiramisu for at least 6 hours, or overnight, to allow the flavors to meld and the dessert to set.