FOR THE STRAWBERRY CAKE:
1 cup whole strawberries — divided (fresh, or frozen and thawed), plus additional for garnish
1 1/2 cups all-purpose flour
1 teaspoon baking powder
1/4 teaspoon kosher salt
1/4 cup whole milk — at room temperature
1 1/2 teaspoons pure vanilla extract
1/2 cup unsalted butter — at room temperature (1 stick)
1 cup granulated sugar
2 large egg whites — at room temperature
1 large egg — at room temperature
FOR THE STRAWBERRY CREAM CHEESE FROSTING:
2 tablespoons unsalted butter — at room temperature
3 ounces reduced-fat cream cheese — at room temperature
2 cups powdered sugar — plus additional if you prefer a sweeter or stiffer frosting
1 tablespoon strawberry puree — reserved from cake recipe
1 pinch kosher salt
1/4 teaspoon pure vanilla extract
Preheat the oven to 350 degrees F. Line the bottom of a 9-inch round cake pan with parchment paper, then lightly coat with nonstick spray. Set aside.
Place the strawberries in a food processor or blender and pulse until pureed. Set 1 tablespoon aside for the frosting, then measure out an additional 1/3 cup for the cake. If you are a little short of 1/3 cup, blend in a few more strawberries as needed.
In a medium bowl, whisk together the flour, baking powder, and salt. Set aside. In a small bowl, whisk together the milk, vanilla, and 1/3 cup strawberry puree. Set aside.
In the bowl of an stand mixer fitted with the paddle attachment (or a large mixing bowl), cream the butter on medium-high speed until it is light and fluffy. Slowly add the granulated sugar and continue to beat until fluffy and well combined. Stop the mixer and add the egg whites. Beat on medium, just until incorporated. Add the whole egg and mix again, just until combined.
With the mixer on low, slowly add half the flour mixture and mix just until the flour disappears. Add in all of the strawberry mixture and mix just until combined. Slowly add the remaining flour mixture, scraping down the sides of the bowl with a spatula as needed. Stop mixing as soon as the flour disappears. If you have a bit of flour stuck to the bottom or sides of the bowl, finish stirring it in by hand.
Pour the batter into your prepared pan and smooth the top. Bake until a toothpick inserted in the center of the cake comes out clean and the top springs back lightly when touched, about 30 to 35 minutes. Place the pan on a cooling rack and let the cake cool in the pan completely. Do not be tempted to frost the cake before it is cool, or the frosting will turn into a big melty mess.
While the cake cools, prepare the frosting: In the bowl of a stand mixer fitted with the paddle attachment or a large mixing bowl, beat the butter on medium speed until smooth and fluffy. Beat in the cream cheese, stopping as soon as the two are fully combined. Reduce the mixer speed to low, then gradually add the powdered sugar. Once it all has been added, increase the mixer speed to medium and continue beating until the frosting is smooth. Don’t overbeat it—once it looks nice and creamy and evenly blended, it’s time to stop. Beat in the strawberry puree, salt, and vanilla until evenly combined. If you’d like the frosting stiffer or sweeter, gradually beat in additional powdered sugar until your desired stiffness/sweetness is reached.
To serve: Transfer the cake from the pan to a serving plate. Tuck strips of waxed or parchment paper underneath the bottom of the cake to keep the plate clean. Spread the frosting generously all over the top of the cake, then down and around the sides. Garnish with fresh berries as desired. Remove the strips of paper and refrigerate until ready to serve. Prior to serving, let the cake stand at room temperature for at least 15 minutes.