For the Cake
- 1 cup unsalted butter, at room temperature
- 2 cups granulated sugar
- 6 large egg whites, at room temperature
- 2 1/ 2 cups buttermilk, at room temperature
- 1 teaspoon vanilla extract
- 1 teaspoon almond extract
- 3 1/ 4 cups cake flour
- 3 1/ 2 teaspoons baking powder
- 1 teaspoon kosher salt
For the Buttercream
- 1 1/ 2 cups unsalted butter, at room temperature
- 3 cups powdered sugar
- 1 tablespoon meringue powder, optional
- 1 1/ 2 teaspoons vanilla extract
- 1/ 8 teaspoon kosher salt
- 3 tablespoons milk, or cream, if needed
- 1 package chocolate sandwich cookies
To Make the Cake
Preheat the oven to 350ºF and grease three 8-inch round cake pans.
In the bowl of your stand mixer fitted with the paddle attachment, cream the butter and sugar for 10 minutes, scraping the bowl down every few minutes, until very light and fluffy.
In a separate bowl, whisk together the egg whites, buttermilk and extracts, just to combine. With the mixer on low, add the wet ingredients to the butter/sugar mixture and mix for 1 minute to combine; it will look lumpy/curdled. Add the flour, baking powder and salt to the mixture; mix on low for 30 seconds, and then beat on medium speed for 2 minutes for a light and airy batter.
Divide the batter between the cake pans. Bake for 25-27 minutes until the centers are done, then set the pans on a wire rack, cover loosely with a clean kitchen towel and cool completely.
To Make the Buttercream
In the bowl of your stand mixer fitted with the whisk attachment, beat the butter for 1 minute until smooth. With the mixer on low, add the powdered sugar, meringue powder and salt and mix until combined. Add the vanilla and milk; increase the speed to medium high and whip for 4-5 minutes, scraping the bowl occasionally, until very light and fluffy.
Reserve 8-10 whole sandwich cookies to decorate the top of the cake. Roughly chop the rest of the cookies and set aside.
When the cakes are cool, run a knife around the edges and remove from the pans. Set one cake layer on a cake board or pedestal. Frost with a layer of buttercream, then generously sprinkle the top of the cake layer with cookies; repeat with the next layers, so that each layer is filled with frosting and cookies. Frost the cake all over with a thin crumb coat of buttercream, then chill for 20 minutes.
Take the remaining chopped cookies and chop more finely so that you don't have any huge pieces left, then mix into the remaining buttercream. Frost the cake with the cookie buttercream and decorate the top with whole cookies.
This cake is best made one day in advance (and stored un-cut in an air-tight container), which gives the cookies time to absorb some moisture from the cake so that they soften slightly. Although I only added cookies to the buttercream and not to the cake batter, you can certainly fold chopped cookies into the cake batter as well, if you like.