Prepare 3 six-inch round cake pans with cake goop or parchment paper.
Add the white cake mix, flour, sugar, salt, sour cream, melted butter, milk, egg whites, and vanilla into the bowl of a stand mixer with the paddle attachment and mix for 2 minutes on medium speed.
Divide the batter into 2 of the 3 prepared pans, if you are using a scale each pan should hold about 17 ounces (or 3 cups) of batter. Leave the remaining third of the batter in the mixing bowl.
Add ¼ cup of the strawberry reduction and the (optional) ½ teaspoon of strawberry emulsion to the reserved batter and stir until combined. Add a drop of red food coloring (optional) to counteract the berries turning slightly purple when they bake.
Pour the strawberry cake batter into the third prepared pan.
Bake the cake layers at 335°F for 30-35 minutes or until a toothpick inserted comes out clean. The strawberry cake may finish before the white cakes. The added liquid changes the chemistry slightly.
Let the cakes cool until you can touch them (about 10 minutes) and flip them out onto a cooling rack until completely cooled.
Wrap in plastic wrap and flash freeze for up to an hour before layering the cake.