How to Make It
Preheat the oven to 350°. Spray two 8-inch cake pans with nonstick cooking spray and line the pans with parchment paper.
In a medium bowl, sift the cake flour with the baking powder and salt. In a food processor, puree the strawberries until smooth, 2 to 3 minutes; you should have ¾ cup of puree. In a medium bowl, whisk the egg whites with the milk and vanilla.
In a large bowl, using a handheld mixer, cream the butter with the sugar until light and fluffy, about 3 minutes. Add the strawberry puree to the bowl and beat at moderate speed until fully incorporated, about 2 minutes. At low speed, beat in the dry ingredients and the egg white mixture in 3 alternating batches.
Divide the batter evenly between the two prepared pans and bake for about 30 minutes, until a toothpick inserted in the center of each cake comes out clean. Transfer the cakes to a rack and let cool in the pans for 20 minutes. Invert the cakes onto the rack; peel off and discard the parchment paper. Let the cakes cool completely.
In a medium bowl, using a handheld mixer, beat the butter at medium speed until smooth. Add the confectioners’ sugar and salt and beat at low speed until just incorporated, about 2 minutes. Add the milk and vanilla and beat at moderate speed until light and fluffy, 3 to 4 minutes more.
Place one cake on a platter. Spread half of the buttercream in an even layer on top of the cake. Arrange strawberries slices in concentric circles on top of the buttercream. Cover with the second cake and spread the remaining buttercream on the top. Decorate with the remaining strawberries.