Preheat oven to 350° F. Prepare cake pans with nonstick cooking spray and parchment circles (see pan sizes in FAQ).
In the bowl of a stand mixer fitted with a paddle attachment or a mixing bowl with an electric hand mixer, mix together all-purpose flour, granulated sugar, baking powder, baking soda, and salt on low speed until combined.
Add cubed room temperature butter one piece at a time while mixing on low speed until all the butter is added. Continue to mix until the mixture resembles wet sand and is crumbly.
Turn the mixer off. Add in egg whites, sour cream, vanilla extract and strawberry reduction. Turn the mixer to medium speed and mix for one minute.
Turn the mixer to low speed and slowly drizzle in the buttermilk. Once all the buttermilk is added, scrape the sides and bottom of the mixing bowl to ensure all the ingredients are well incorporated. Mix for an additional 30 seconds on low speed.
Portion the cake batter into the prepared cake pans. Use a kitchen scale to ensure the layers have equal amounts of batter.
Bake the cake layers for 25-30 minutes. The cake layers are done baking when an inserted toothpick comes out clean or the cake bounces back when gently poked.
Remove the pans from the oven. Allow the cake layers to cool in the pans for 15 minutes before removing the cake and transferring to a wire rack to cool completely.