For the Cake

Preheat your oven to 350°F (175°C). Grease and flour two 9-inch cake pans or line them with parchment paper. In a medium bowl, sift together the cake flour, baking powder, and kosher salt. Set aside.

In a large bowl, use an electric mixer to cream the softened unsalted butter and granulated sugar together until the mixture is light and fluffy (about 3-4 minutes).

Add the eggs and egg whites one at a time, beating well after each addition. Mix in the scraped vanilla bean seeds and the vanilla extract until combined. In a separate small bowl or measuring cup, whisk together the vegetable oil and buttermilk.

With the mixer on low speed, add the dry flour mixture to the butter mixture in three additions, alternating with the buttermilk and oil mixture (start and end with the flour). Mix just until combined; do not over mix.

Evenly divide the batter between the prepared pans and smooth the tops. Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cakes to cool in the pans for about 10 minutes. Then, turn them out onto a wire rack to cool completely before frosting.

Frosting Preparation

Using a mixer beat the softened butter until smooth and creamy. Gradually add powdered sugar, beating on low speed until combined. Add the vanilla extract and scraped vanilla bean seeds.

Add milk or cream one tablespoon at a time until the frosting reaches a spreadable consistency. Once the cake layers are completely cool, spread the frosting evenly on the top of one layer.

Place the second layer on top and frost the top and sides of the cake as desired.