In a stand mixer, combine ½ cup of pasteurized egg whites with 3½ cups of powdered sugar. Mix on low speed until everything is just incorporated, then switch to medium-high for about 5 minutes. You'll know it’s ready when stiff peaks form and the mixture is glossy.

Change to the paddle attachment and begin adding 1½ cups of room-temperature unsalted butter in small chunks. Keep mixing on low speed until the butter is fully incorporated. Once combined, increase the speed to medium and beat for another 5 minutes until the buttercream is fluffy and light in texture.

Add 1 tablespoon of vanilla extract, 2 tablespoons of sifted matcha powder, and ½ teaspoon of fine salt. Mix on low speed until fully combined, ensuring even distribution throughout the buttercream.

If the frosting appears to have separated, continue mixing on low speed until it smooths out completely. Gently fold in the buttercream to ensure the texture is perfect for spreading.