Step 1

Preheat oven to 325°F. Line and grease three 6-inch cake pans with parchment rounds.

Step 2

Add the unsalted butter and granulated sugar into the bowl of a stand mixer. Beat on a high speed with a whisk attachment for a few minutes, scraping down the sides of the bowl as need with a rubber spatula. The mixture will become lighter in color as air is whipped into it.

Step 3

Add the egg whites, and mix at a medium speed until they're incorporated.

Step 4

Sift the dry ingredients (cake flour, baking powder, matcha powder, and salt) into a separate bowl.

Step 5

Add half of the dry ingredients into the butter mixture, and mix on a low speed until just incorporated.

Step 6

Add the sour cream, oil and vanilla extract. Mix at a low speed until combined, scraping the sides and bottom of the bowl as needed!

Step 7

Mix in the remaining dry ingredients on a low speed.

Step 8

Divide batter evenly between the prepared cake pans. I like to use a digital kitchen scale to weigh my pans, to make sure my layers will be the same height.

Step 9

Bake for 35 minutes, or until a toothpick comes out with a few moist crumbs. Rotate pans halfway through to help them bake evenly.

Step 10

Allow the pans to cool for 10 minutes, then run an offset spatula around perimeter of the pan to separate the cake from the pan.

Step 11

Place cake layers into the freezer for 45 minutes, to accelerate the cooling process. Once the layers are fully cooled, carefully flip the pans and remove the layers from the pans.

Step 12

Use a serrated knife to level the tops, and trim the sides to remove any caramelization.

Step 13

While the cake layers bake and cool, make the fluffy buttercream frosting.

Step 14

Place the room temperature pasteurized egg whites and powdered sugar in the bowl of a stand mixer (or a large bowl if you plan to make with a hand mixer).

Step 15

Mix on a low speed to combine.

Step 16

Once incorporated, mix on medium high with a whisk attachment for 5 minutes until stiff peaks have formed.

Step 17

Swap the whisk attachment for a paddle attachment. This will help make your buttercream be smooth once it's fully made.

Step 18

Mix in pieces of room temperature butter on a low speed in 2 additions.

Step 19

Once the butter is incorporated, mix on medium speed for an additional 5 minutes.

Step 20

Add in 1 Tbsp of vanilla extract and 1/2 tsp of salt. Mix until the buttercream is fluffy and smooth.

Step 21

If you frosting breaks in the beginning when you add the butter, don't worry! Just keep mixing it, and it should come together in a few minutes.

Step 22

Stir for an additional few minutes by hand with a rubber spatula to get it silky smooth. Set aside.

Step 23

While the cake chills with its second coat of frosting, make the matcha white chocolate ganache.

Step 24

Heat heavy cream in a heat proof bowl in the microwave for 45 seconds, until it's just beginning to bubble.

Step 25

Gently pour white chocolate chips into the heavy cream, making sure they are fully covered with cream. Allow mixture to sit for 1 minute.

Step 26

Stir slowly until the cream and white chocolate are combined. Some bits of chocolate may not be fully melted yet. Heat the mixture again for 20 seconds, and stir.

Step 27

Repeat as necessary until all the white chocolate bits are fully melted and incorporated.

Step 28

Mix in the matcha powder. Allow to cool until desired viscosity is reached (barely warm to the touch).

Step 29

If it seems too thin or thick, you can add a touch more chocolate chips or heavy cream! The type of cream and white chocolate that you use can affect the consistency, so feel free to adjust as needed.

Step 30

Stack and frost cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board.

Step 31

Add an even layer of buttercream on top of the first cake layer. Stack and frost remaining cake layers.

Step 32

Spread a thin coat of frosting around the the cake, to fully cover the cake layers.

Step 33

Smooth using a bench scraper, then chill the cake in the fridge (30 minutes) or freezer (10 minutes) until the frosting is firm to the touch.

Step 34

Add a second, thicker layer of buttercream frosting to the cake, and chill the cake again in the fridge (20 minutes) or freezer (5 minutes) until the frosting is firm to the touch.

Step 35

Use a spoon to add the ganache drips around the cake with the white chocolate matcha ganache.

Step 36

Place the remaining frosting into a small piping bag fit with an Ateco 869 frosting tip. Pipe dollops around the top of the cake, and dust with an extra bit of matcha powder.