10 ounces (2 cups) frozen whole strawberries
¾ cup whole milk, room temperature
6 extra large egg whites, room temperature
2 teaspoons vanilla extract
2¼ cup (9 ounces) cake flour
1¾ cups (12½ ounces) granulated sugar
4 teaspoons baking powder
1 teaspoon kosher salt
12 tablespoons (6 ounces) unsalted butter, cut into 12 pieces, softened
10 tablespoons (5 ounces) unsalted butter, softened
2¼ cups (9 ounces) confectioners' sugar
12 ounces cream cheese, cold and cut into pieces
2 teaspoons vanilla extract
Pinch of kosher salt
8 ounces fresh strawberries, hulled and sliced thin (about 1½ cups)
For the cake: Heat the oven to 350 degrees. Line the bottoms of two 9-inch round cake pans with parchment paper and lightly spray with non-stick baking spray.
Transfer frozen strawberries to a microwave-safe bowl and microwave until the strawberries are soft and have released their juice, about 5 minutes. Place the strawberries in a fine-mesh strainer set over a small bowl. Firmly press fruit dry (juice should measure ¾ cup); reserving strawberry solids.
Transfer juice to a small saucepan and bring to a boil over medium-high heat; cook stirring occasionally until syrupy and reduced to ¼ cup, 6-8 minutes. Remove from the heat and stir in milk to combine.
Whisk strawberry milk, egg whites and vanilla in a bowl. Using a stand mixer fitted with the paddle attachment, mix flour, sugar, baking powder and salt on low speed until combined. Add butter, 1 piece at a time, and mix until only pea-size pieces remain, about 1 minute. Add half of milk mixture, increase speed to medium-high, and beat until light and fluffy, about 1 minute. Reduce speed to medium-low, add remaining milk mixture and beat just until incorporated, about 30 seconds. Give the batter a final stir by hand.
Divide the batter evenly into the prepared pans and bake until the cakes are lightly golden, about 20-25 minutes. Cool cakes in the pan on a wire rack for 10 minutes. Remove the cakes from the pans, discarding parchment, and cool completely, about 2 hours. (Cooled cakes can be wrapped with plastic wrap and stored at room temperature for up to 2 days.)
For the frosting: Using a stand mixer fitted with the paddle attachment, mix butter and sugar on low speed until combined, about 30 seconds. Increase speed to medium-high and beat until pale and fluffy, about 2 minutes. Add cream cheese one piece at a time and beat until incorporated, about 1 minute. Add reserved strawberry solids, vanilla extract, and salt and mix until combined, about 30 seconds. Use immediately or refrigerate until ready to use for up to 2 days.
Pat the strawberry slices dry with paper towels. Place one cooled cake round on a serving plate. Spread ¾ cup frosting over the top of the cake. Press 1 cup of strawberries in an even layer over the frosting and cover with an additional ¾ cup frosting.
Place the second cake round on top and spread remaining frosting over the top and sides of cake. Garnish the cake with the remaining strawberry slices. (Cake can be refrigerated for up to 2 days. Bring to room temperature before serving.)