Purée: Blend 1 pound of rinsed and hulled strawberries until smooth. You should have just over 1 cup of purée
Reduce: Simmer the purée in a saucepan over medium-low heat, stirring occasionally, until it reduces to ½ cup (about 135 g). This process takes about 25 to 35 minutes, or longer if the strawberries are very juicy.
Cool: Allow the purée to cool completely before using in the cake batter. It can be prepared a day in advance and stored in the refrigerator. Bring it to room temperature before adding it to the batter.
Prepare the Pans: Preheat your oven to 350°F (177°C). Grease two 9-inch round cake pans, line them with parchment paper, then grease the parchment paper to ensure the cakes release smoothly.
Mix Dry Ingredients: In a bowl, whisk together the cake flour, baking powder, baking soda, and salt. Set aside.
Cream Butter and Sugar: In a large bowl, use an electric mixer to cream the softened butter and sugar on high speed until light and fluffy (about 2 minutes). Scrape down the sides of the bowl as needed.
Add Egg Whites: Add the egg whites one at a time, beating on high speed until well combined (about 2 minutes).
Add Sour Cream and Vanilla: Mix in the sour cream (or yogurt) and vanilla extract until combined.
Incorporate Dry Ingredients: With the mixer on low speed, add the dry ingredients in three parts, alternating with the milk, mixing just until combined. Avoid overmixing.
Add Strawberry Purée: Gently fold in ½ cup of the cooled reduced strawberry purée. If desired, add 1-2 drops of pink or red food coloring to enhance the color. Mix just until incorporated.
Bake: Divide the batter evenly between the prepared pans. Bake for about 24 to 25 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool completely in the pans on a wire rack.
Make Strawberry Powder: Grind the freeze-dried strawberries into a fine powder using a blender or food processor. You should have about ½ cup of strawberry powder.
Cream Cream Cheese: In a large bowl, beat the cream cheese on high speed for 1 minute until smooth and creamy.
Add Butter: Add the butter and beat until well combined.
Add Remaining Ingredients: Add the confectioners’ sugar, strawberry powder, 1 tablespoon of milk, and vanilla extract. Beat on medium-high speed until smooth and creamy. Adjust the consistency with an extra tablespoon of milk if needed. Taste and add a pinch of salt if desired.
Level the Cakes: Use a serrated knife to slice a thin layer off the tops of the cakes to create a flat surface.
Assemble: Place one cake layer on your serving plate. Spread an even layer of frosting over the top. Place the second layer on top and cover the entire cake with the remaining frosting.
Chill: Refrigerate the cake for at least 45 minutes before slicing to help it hold its shape.