Preheat your oven to 350°F (175°C) and prepare two 8-inch round cake pans by greasing them with unsalted butter and lining the bottoms with parchment paper.

In a large mixing bowl, sift together cake flour, granulated sugar, matcha powder, baking powder, and fine salt.

Add softened unsalted butter to the dry mixture and mix until crumbly. Next, pour in the egg whites, sour cream, vegetable oil, and vanilla extract, blending until smooth.

Divide the batter evenly between the two prepared cake pans and bake for 35-40 minutes.

Allow the cakes to cool for about 10 minutes before transferring them to a wire rack to cool completely.

For the buttercream, whip egg whites and granulated sugar over simmering water until warm, then whip until stiff peaks form.

Gradually mix in softened butter until smooth, then add strawberry jam, lemon juice, and freeze-dried strawberry powder.

Place one layer of the cooled cake on a plate, spread with buttercream, and add a layer of strawberry jam before placing the second cake layer on top.

Frost the entire cake with remaining buttercream and decorate as desired.