Preheat your oven to 350 degrees F. Prepare an 8-by-8-inch square baking pan by lightly oiling it and lining it with parchment paper. Make sure to leave overhang on two edges for easy removal later.
In a large mixing bowl, whisk together the egg yolks and half of the granulated sugar until smooth and lightened. While whisking, drizzle in the vegetable oil until fully incorporated.
Combine the matcha powder and sakura leaf powder in a small bowl, drizzle in about 1 tablespoon of whole milk and whisk until smooth.
Pour the matcha mixture into the egg yolk mixture and stir until combined. Sift the cake flour and fine sea salt over the mixture and fold until fully incorporated.
In a separate bowl, whip the egg whites with an electric mixer until frothy. Gradually add the remaining granulated sugar and beat until soft peaks form.
Fold one-third of the whipped egg whites into the batter to lighten it, then gently fold in the remaining whites until no streaks remain.
Pour the batter into the prepared baking pan and spread it evenly. Gently drop the pan to release air bubbles and level the top.
Bake for 13 to 15 minutes or until a toothpick comes out clean. Remove from oven and let cool completely on a wire rack.
Use a round cake cutter to cut a 6-inch round from the cooled cake and place it inside a cake ring lined with acetate.
For the mousse, cut the gelatin into strips and soak in cool water. Heat whole milk in the microwave until steaming.
Add the softened gelatin to the hot milk and whisk until dissolved. In a bowl, combine mascarpone cheese and the milk-gelatin mixture, whisking until smooth.
In another bowl, whip the heavy whipping cream until it shows texture but doesn’t hold soft peaks yet. Fold one-third into the mascarpone mixture, then fold in the remaining cream until incorporated.
Transfer half of the whipped cream mixture to another bowl and mix in the strained cherry purée or food coloring.
Scoop about one-third cup of white mousse onto the center of the cake, then layer with one-third cup of pink mousse. Repeat to build up layers.
Refrigerate until set, at least 3 hours or overnight. Remove the ring and slice using a hot knife before serving.
