Preheat the oven to 350°F. Line 2, 8-inch round cake pans with parchment paper and spray with nonstick cooking spray. Set aside.

In a large bowl, whisk together the cake flour, baking powder, and salt. Set aside.

In the bowl of a stand mixer with the paddle attachment, cream together butter, sugar, and both extracts until light and fluffy, about 5 minutes. Stop to scrape down the sides of the bowl as needed.

With the mixer on the lowest speed, carefully add in egg whites, one at a time, beating well after each addition, stopping to scrape down the sides of the bowl as needed.

With the mixer still on low, add ⅓ of the flour mixture into the creamed mixture, then half the milk, another third of the flour mixture, the remaining milk, and then the remaining flour mixture. Mix just until combined. Stop to scrape down the sides of the bowl as needed.

Distribute the batter evenly into the two prepared pans. Bake for 26-28 minutes, or until a toothpick inserted in the center comes out clean. Allow the cake to cool completely on a wire rack.

To the bowl of a stand mixer with the paddle attachment, add the butter, sugar, salt, and any added flavorings.

Start mixing on low speed until the sugar is incorporated with the butter. Increase the mixing speed to high and beat until smooth and fluffy, about 2 minutes.

Adjust the consistency with milk as needed.

Store unused buttercream in the refrigerator in an airtight container until ready to use. Bring it back to room temperature before using to pipe or frost the cooled cake.