Preheat the oven to 350°F (177°C).
Line the bottom of two 8-inch cake pan with parchment paper. Then, spray the pans with cooking spray to prevent the cake from sticking.
Crush the freeze-dried strawberries in a blender or using a rolling pin into a fine powder. Sift through fine-mesh sieve. (Note: You’ll end up with roughly 65g of strawberry powder.)
In a medium bowl, whisk together milk, sour cream, and vanilla.
In a mixing bowl with the paddle attachment, mix powdered freeze-dried strawberries, flour, sugar, baking powder, and salt on low speed.
Add butter and continue to mix on low speed until no dry ingredients are left, about 3 minutes.
Add the egg whites and mix on medium speed until combined, about 1 minute.
Add half of the milk mixture and beat on medium speed for 1 ½ minutes.
Then add the remaining milk mixture and continue to beat for another minute, scraping the sides of the bowl halfway.
Pour the batter evenly into the prepared pan and smooth the top. Bake the cake for 23-28 minutes, or until the cake are light golden and the inserted toothpick comes out clean.
Let the cake rest in the pan for 3 minutes. If needed, loosen the edges with a knife and invert the cakes onto a wire rack to cool completely. (At this point, cake layer can be wrapped and stored at room temperature for up to 1 day or frozen for up to 1 month.)