NOTE: It is SUPER IMPORTANT that all the room temperature ingredients listed above are room temperature and not cold or hot. If your ingredients just came out of the refrigerator or the strawberry puree is too hot, your mixture could curdle during the process of making the cake batter and become ruined. Adjust an oven rack to the middle position and preheat to 350ºF/176ºC.
Grease two 6" cake pans and one 4" cake pan with cake goop or other preferred pan release.
Add butter to stand mixer and beat at medium-high speed until smooth and shiny, about 30 seconds. Gradually sprinkle in the sugar, beat until mixture is fluffy and almost white, about 3-5 minutes. Add the egg whites approximately two at a time, beating 30 seconds between.
Whisk the flour, baking powder, baking soda, salt, and lemon zest in a medium bowl.
Combine the strawberry reduction, milk, vanilla extract, lemon extract, strawberry extract and food coloring in a separate medium bowl.
With the mixer at the lowest speed, add about a third of the dry ingredients to the batter, followed immediately by about a third of the milk mixture, mix until ingredients are almost incorporated into the batter. Repeat the process 2 more times. When the batter appears blended, stop the mixer and scrape the sides of the bowl with a rubber spatula.
Divide the batter evenly between the prepared pans. Smooth the tops with a rubber spatula. Bake cakes until they feel firm in the center and a toothpick comes out clean or with just a few crumbs on it, about 35-40 minutes.
Transfer pans to a wire rack and let cool for 10 minutes. Invert cakes onto the rack and pop cakes out of pans. Cool completely before frosting.