Make the Sponge Cake:

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and line a round cake pan (8-inch) with parchment paper. Grease the sides of the pan to ensure the cake does not stick.
2. Beat the Eggs and Sugar: In a large mixing bowl, beat the eggs and sugar together with an electric mixer on medium speed until the mixture becomes light and fluffy. This may take about 5-7 minutes.
3. Add Vanilla and Oil: Mix in the vanilla extract and vegetable oil, and continue beating until fully incorporated.
4. Combine Dry Ingredients: In a separate bowl, sift together the flour, matcha powder, and baking powder.
5. Fold in Dry Ingredients: Gradually fold the dry ingredients into the wet ingredients using a spatula or a whisk, being careful not to deflate the batter.
6. Add Warm Water: Slowly incorporate the warm water into the batter, mixing gently until smooth.
7. Bake the Cake: Pour the batter into the prepared cake pan. Bake in the preheated oven for 20-25 minutes or until the top is golden brown and a toothpick inserted comes out clean.
8. Cool the Cake: Allow the sponge cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

Make the Yuzu Cream:

9. Whip the Cream: In a chilled bowl, whisk the heavy cream until soft peaks form using an electric mixer.
10. Add Yuzu Flavor: Gradually add the yuzu juice and powdered sugar to the whipped cream and continue whisking until stiff peaks form and the cream is thick and fluffy.
11. Optional Zest: For an extra burst of citrus flavor, fold in the yuzu zest.

Assemble the Cake:

12. Frost the Cake: Once the cake has completely cooled, spread a generous layer of the yuzu cream on top of the cake. You can also slice the cake into two layers and add cream between them for a layered effect.
13. Chill and Set: Refrigerate the cake for 30 minutes to let the yuzu cream firm up and the flavors meld.