Blend strawberries and milk until completely smooth
Strain through a fine-mesh sieve to remove seeds
Transfer to a saucepan and cook over medium-low heat, stirring often, for 8–10 minutes until slightly thickened and reduced
Cool completely and measure 1¼ cups (300g) for the cake
Combine cake flour, baking powder, baking soda, salt, and freeze-dried strawberry powder
Cream together butter and sugar until light and fluffy
Mix in oil, egg, and egg whites
Alternate adding dry ingredients and strawberry milk mixture to the wet ingredients
Stir in vanilla extract and sour cream
Bake according to temperature and time (not provided in excerpt)
