Preheat oven to 350°F (177°C). Grease three 9-inch cake pans, line with parchment paper rounds, then grease the parchment paper.

Whisk the cake flour, salt, baking powder, and baking soda together. Set aside.

Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the butter and sugar together on high speed until smooth and creamy, about 3 minutes.

Beat in the 3 eggs, 2 egg whites, and vanilla extract on high speed until combined, about 2 minutes.

With the mixer on low speed, add the dry ingredients just until combined. With the mixer still running on low, pour in the buttermilk and mix just until combined.

Pour batter evenly into cake pans. Bake for around 23-26 minutes or until the cakes are baked through.

Allow cakes to cool completely in the pans set on a wire cooling rack.

In a large bowl using a handheld mixer or stand mixer fitted with a whisk or paddle attachment, beat the butter on medium speed until creamy, about 2 minutes.

Add confectioners’ sugar, milk, vanilla extract, and salt with the mixer running on low. Increase to high speed and beat for 2 minutes.

Using a large serrated knife, slice a thin layer off the tops of the cakes to create a flat surface.

Place 1 cake layer on your cake stand, evenly cover the top with about 1 and ½ cups of frosting. Top with 2nd cake layer and evenly cover the top with about 1 and ½ cups of frosting. Top with the third cake layer.

Spread the remaining frosting all over the top and sides.

Refrigerate cake for at least 1 hour before slicing.