For the Vanilla Bean Cake:
3 sticks (1 ½ cups) unsalted butter, at room temperature (on counter apprx 20 minutes)
2 2/3 cups granulated sugar
9 egg whites, at room temperature
4 ½ cups all-purpose flour
2 tbsp baking powder
1 tsp salt
2 cups buttermilk
1 vanilla bean, split and seeds scraped
1 teaspoon pure vanilla extract
For the buttercream frosting:
3 ½ sticks (1 ½ cups) unsalted butter, softened and cut into cubes
3 ½ cups sifted confectioners’ sugar
¼ cup heavy cream
1 ½ tsp pure vanilla extract
1/8 tsp salt
Ateco or Wilton color gel for dying
To make the cake: Preheat oven to 350° F. Butter three 8" x 2" round cake pans, line with parchment rounds, butter the rounds, and dust the pans and rounds with flour, tapping out the excess.
In a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium-high speed until lighter in color and slightly increased in volume, 3 to 5 minutes. Lower the speed to medium and add the egg whites gradually, mixing until fully incorporated.
Sift the flour, baking powder, and salt into a medium bowl. Mix vanilla extract and vanilla bean seeds into buttermilk. Alternate dry ingredients and buttermilk into creamed mixture, beginning and ending with dry ingredients. Mix until just incorporated or finish by hand gently.
Divide the batter evenly between the prepared pans. If possible, weigh the batter in each cake pan on a digital kitchen scale to ensure even layers. Smooth with small offset palette knife, and bake for about 30 minutes, rotating once after 20 minutes. Cake is done when toothpick or skewer comes clean.
Let pans cool on wire rack for 10 minutes, then invert cakes onto racks, gently, peeling away parchment rounds. Let cool completely.
To make the frosting: In the bowl of a stand mixer fitted with the whisk attachment, whip butter on medium-high speed until smooth, about 1 minute.
Add the confectioners’ sugar to the bowl and mix on medium-low speed just until incorporated. Add in the salt. Continue to beat on medium-high speed until smooth, about 1 to 2 minutes. Mix in the vanilla extract and heavy cream on low speed just until incorporated. Increase the mixer speed and whip on high speed until light and fluffy, scraping down the bowl as needed, about 4 minutes. Stir in the color gel to achieve your desired color.
Frost and decorate the cake as desired.