Strawberry Puree: Hull the strawberries, place them in a blender, and puree on high for about 30 seconds, or until completely smooth.
Reduce Puree: Transfer the strawberry puree to a small saucepan and bring it to a simmer over medium heat, stirring frequently. Continue cooking until the puree has reduced by about half, which takes about 25 minutes for fresh strawberries or up to 45 minutes for frozen strawberries. The finished reduction should yield about 1 cup. Cool Puree: Allow the strawberry reduction to cool completely before dividing it between the cake batter and frosting.
Prepare Pans: Preheat the oven to 350°F. Butter two 9-inch round cake pans or coat them with baking spray, then line the bottoms with parchment paper. If desired, wrap the pans with soaked fabric baking strips.
Combine Dry Ingredients: In a large bowl, whisk together the flour, baking powder, salt, and baking soda until evenly combined.
Cream Butter: Using a stand mixer fitted with the paddle attachment or an electric mixer, beat the softened butter on medium speed just until creamy.
Add Sugar: Add the granulated sugar to the butter and continue beating until the mixture is light and fluffy, about 5 minutes.
Add Egg Whites: Scrape down the sides of the bowl, then add the egg whites and vanilla. Beat on medium speed for about 1 minute, or until the mixture is well combined and very fluffy.
Combine Batter: Reduce the mixer speed to low. Add the flour mixture alternately with the milk and strawberry reduction, mixing only until the ingredients are combined. Stop to scrape down the bowl as needed during mixing.
Add Color: If desired, mix in a drop or two of pink food coloring until the batter reaches the preferred color.
Fill Pans: Divide the batter evenly between the two prepared cake pans.
Bake Cakes: Bake at 350°F for 30 minutes, or until the cakes feel springy when touched and begin pulling away from the sides of the pans.
Cool in Pans: Let the cakes cool in their pans for 20 minutes.
Finish Cooling: Remove the cakes from the pans and transfer them to a wire rack. Allow them to cool completely, then discard the parchment paper.
Beat Frosting Base: In a large mixing bowl or stand mixer fitted with the paddle attachment, beat the cream cheese, butter, vanilla, and salt until smooth and fluffy, about 5 minutes.
Add Powdered Sugar: With the mixer running on low speed, gradually add the sifted powdered sugar, alternating it with a tablespoon of strawberry puree. Stop and scrape down the bowl several times during mixing.
Fluff Frosting: Once all the powdered sugar has been incorporated, increase the mixer speed to medium and beat until the frosting is fluffy. If it is too stiff rather than silky, add another tablespoon or two of strawberry puree or milk.
Layer Cake: Place one completely cooled cake layer on a cake stand and spread about 1 cup of strawberry frosting evenly over the top.
Stack Cake: Place the second cake layer on top of the frosted first layer.
Frost Cake: Spread the remaining frosting over the top and sides of the assembled cake.
Decorate Cake: Decorate the frosted cake as desired before serving or storing.
Store Cake: Keep the finished cake covered. According to the source, it will keep at room temperature for up to 5 days.
