Instructions:
- Preheat oven to 350°F (175°C). Grease and line the bottoms of three 8-inch cake pans with parchment paper rounds. Dust lightly with flour.
- Sift the cake flour, sugar, baking powder, and salt into a large bowl. Whisk thoroughly to combine evenly.
- Add the softened butter to the dry ingredients. Beat on medium-low speed until the mixture resembles coarse, wet sand.
- In a separate bowl, lightly whisk the room-temperature milk and clear vanilla extract.
- Slowly pour about half of the milk mixture into the flour/butter mixture while mixing on low speed until just combined. Scrape down the sides.
- In a clean, grease-free bowl, whip the egg whites until medium-stiff peaks form.
- Add the remaining milk mixture to the batter and mix briefly. Stop the mixer. Gently fold in one-third of the whipped egg whites to lighten the batter.
- Gently fold in the remaining egg whites in two additions using a spatula, taking extreme care not to deflate the air.
- Divide batter evenly among the three prepared pans. Bake for 28–32 minutes, or until a skewer inserted in the centre comes out clean. Cool in pans for 10 minutes, then invert onto wire racks to cool completely.
- To make the buttercream, beat the softened butter in a stand mixer until very pale and fluffy (about 5 minutes).
- Gradually add the sifted powdered sugar, one cup at a time, mixing on low speed. Increase speed to medium and beat in the heavy cream, vanilla bean paste, clear vanilla, and salt for a full 3–5 minutes until light and fluffy.
- Level the cooled cake layers. Assemble the cake by spreading a generous layer of frosting between each layer. Apply a thin crumb coat, chill for 20 minutes, then apply the final, smooth coat of buttercream.