Preheat oven to 350°F (175°C). Line a 9-inch (23 cm) round cake pan or a 9x5-inch loaf pan with parchment paper, leaving an overhang for easy removal. Lightly grease the pan under the parchment.

Dry ingredients

In a large bowl, sift together the cake flour, matcha powder, baking powder, and fine sea salt. Whisk in 1/2 cup granulated sugar until evenly combined and no lumps remain.

Wet ingredients

In a separate bowl, whisk the whole milk, buttermilk, egg, melted cooled butter, and 1 teaspoon vanilla extract until smooth.

Combine batter

Make a well in the dry ingredients and pour in the wet mixture. Gently fold with a spatula until just combined — do not overmix. A few small streaks of flour are fine. The batter should be thick but pourable; if too thick, add up to 1 tablespoon milk.

Bake base

Pour batter into the prepared pan and smooth the top. Bake in the preheated oven for 18–22 minutes, or until the top is set and a toothpick inserted into the center comes out with a few moist crumbs. Remove from oven and let cool in pan on a wire rack while you prepare the meringue.

Cloud Meringue Topping

Prepare egg whites

Ensure the mixing bowl and whisk/beaters are completely clean and dry. Separate the 3 room-temperature egg whites into the bowl, discarding or saving yolks for another use.

Whip to soft peaks

Begin whipping the egg whites at medium speed. When they become frothy, add the cream of tartar. Gradually stream in the 1/2 cup granulated sugar over about 1–2 minutes while increasing speed to high. Continue whipping until soft to medium-stiff glossy peaks form (the meringue should hold peaks but still be billowy).

Fold in vanilla

Reduce speed or switch to a spatula and gently fold in 1/2 teaspoon vanilla extract. Do not overfold; keep the meringue airy.

Top the baked base and shape cloud

Spoon the meringue over the cooled green tea base, piling it high in the center to form a cloud-like dome. Use the back of the spoon to create soft peaks and ridges for an airy 'cloud' texture.

Bake meringue

Return the pan to the oven and bake at 350°F (175°C) for 8–12 minutes, or until the meringue is pale golden at the tips and set to the touch. Watch closely to avoid overbrowning. Optional: for a more even color, rotate the pan halfway through.

Cool

Remove from oven and cool completely on a wire rack (about 30–40 minutes). Cooling allows the meringue to set and the interior to stabilize so slices hold shape.

Finishing & Serving

Dust and garnish

Once cooled, lift the Green Tea Cloud piece from the pan using the parchment overhang and transfer to a serving plate. Lightly sift 1/2 teaspoon matcha powder over the top for color and a hint of green-tea aroma. If desired, dust very lightly with 1 tablespoon powdered sugar for contrast.

Garnish (optional)

Arrange edible flowers or microgreens around the base or on top for a delicate presentation.

Slice and serve

Use a sharp knife warmed under hot water and dried between cuts to make clean slices. Serve at room temperature. Store any leftovers in an airtight container at cool room temperature for up to 24 hours (meringue will soften), or refrigerate up to 2 days (note refrigeration will soften meringue more).