2 and 1/2 cups (285g) cake flour (spoon & leveled)
2 teaspoons baking powder
1/2 teaspoon baking soda
1 teaspoon salt
3/4 cup (1.5 sticks; 170g) unsalted butter, softened to room temperature
1 and 3/4 cups (350g) granulated sugar
5 large egg whites, at room temperature
1/3 cup (75g) sour cream or plain yogurt, at room temperature
2 teaspoons pure vanilla extract
1/2 cup (120ml) whole milk, at room temperature*
1/2 cup reduced strawberry puree (see note)*
optional: 1-2 drops red or pink food coloring
Strawberry Cream Cheese Frosting
1 cup (about 25g) freeze-dried strawberries*
one 8-ounce block full-fat cream cheese, softened to room temperature
1/2 cup (1 stick; 115g) unsalted butter, softened to room temperature
3 cups (360g) confectioners’ sugar
1–2 Tablespoons milk
1 teaspoon pure vanilla extract
salt, to taste
Make the reduced strawberry puree and allow it to cool completely. See note. You can make it a few days ahead of time and store it covered in the refrigerator or cover and freeze it for up to 3 months. Thaw before using in the recipe.
Preheat the oven to 350°F (177°C). Grease and lightly flour two 9-inch cake pans.
Whisk the cake flour, baking powder, baking soda, and salt together. Set aside.
Using a handheld or stand mixer fitted with a whisk attachment, beat the butter and sugar together on high speed until smooth and creamed, about 2 minutes. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. Beat in the egg whites on high speed until combined, about 2 minutes. Then beat in the sour cream and vanilla extract. Scrape down the sides and up the bottom of the bowl as needed. With the mixer on low speed, add the dry ingredients until just incorporated. With the mixer still running on low, slowly pour in the milk *just* until combined. Do not overmix. Whisk in 1/2 cup of reduced strawberry puree, making sure there are no lumps at the bottom of the bowl. The batter will be slightly thick. Stir in food coloring, if desired. (I use 1 small drop.)
Pour batter evenly into cake pans. Bake for around 24-25 minutes or until the cakes are baked through. To test for doneness, insert a toothpick into the center of the cake. If it comes out clean, it is done. Allow cakes to cool completely in the pans set on a wire rack. The cakes must be completely cool before frosting and assembling.
Make the frosting: Using a blender or food processor, process the freeze-dried strawberries into a powdery crumb. You should have around 1/2 cup crumbs. Set aside. In a large bowl using a hand-held or stand mixer fitted with a paddle or whisk attachment, beat the cream cheese for 1 minute on high speed until completely smooth and creamy. Beat in the butter until combined. Add the confectioners’ sugar, strawberry powder, 1 Tablespoon milk, and vanilla and beat on medium-high speed until combined and creamy. Add 1 more Tablespoon of milk to slightly thin out, if desired. Taste, then add a pinch of salt if needed. Yields about 3 cups of frosting.
Assemble and frost: First, using a large serrated knife, slice a thin layer off the tops of the cakes to create a flat surface. Discard (or crumble over ice cream!). Place 1 cake layer on your cake stand or serving plate. Evenly cover the top with frosting. Top with 2nd layer and spread the remaining frosting all over the top and sides. Refrigerate for at least 45 minutes before slicing. This helps the cake keep its shape when cutting– it could slightly fall apart without time in the fridge.
Cover leftover cake tightly and store in the refrigerator for 5 days.