Preheat your oven to 350°F. Line a cupcake pan with 12 liners.

In a medium bowl, whisk together the cake flour, baking powder, baking soda, and salt.

In a large bowl, cream the butter and granulated sugar with an electric mixer on high speed until fluffy, about 2-3 minutes.

Add in the egg whites and vanilla. Mix on medium-high speed for 1-2 minutes until pale and smooth.

Gradually add the dry ingredients and buttermilk to the butter mixture, mixing on low speed, then medium speed until combined. The batter will be thick.

Divide the batter evenly among the 12 liners, filling each about two-thirds to three-quarters full.

Bake for 16-18 minutes or until a toothpick comes out clean. Cool the cupcakes in the pan for 10 minutes, then transfer to a cooling rack.

Combine the chopped white chocolate, butter, and heavy cream in a double boiler over boiling water.

Melt the ingredients together, stirring occasionally.

Remove from heat and transfer the ganache to a small bowl.

Let it cool to room temperature, then whip with an electric mixer on high speed until pale and fluffy. Transfer to a piping bag.

In a large bowl, whip the butter and salt with an electric mixer on high speed for 5-10 minutes until pale and fluffy.

Add the melted and slightly cooled white chocolate, mixing on medium speed.

Sift the powdered sugar into the mixture 1/2 cup at a time, mixing on low then medium speed until fully combined. Scrape the bowl as needed. Mix on high speed for 1 minute until light and fluffy. Transfer to a piping bag fitted with a decorative tip.

Once the cupcakes are cool, remove the centers.

Fill each cupcake with white chocolate ganache.

Pipe a generous amount of white chocolate buttercream onto each cupcake. Serve and enjoy!