Set an oven rack in the middle position and heat the oven to 350°F. Grease and flour two 8-inch or 9-inch round cake pans.

Whisk the flour, baking powder and salt together in a medium bowl.

Beat the cake butter and granulated sugar until light and fluffy, about 2 to 3 minutes. Beat in the cake vanilla.

Beat in the eggs and egg white one at a time, letting each one mix in before adding the next. Scrape down the bowl as needed. On low speed, add the flour mixture in 2 parts, alternating with the cake milk.

Blot the finely chopped strawberries dry, then gently fold them into the batter by hand. Divide the batter evenly between the pans.

Bake for about 40 to 44 minutes, until a tester inserted in the center comes out clean and the tops are lightly browned. Cool the cakes completely in their pans on a wire rack before removing and assembling.

Process the freeze-dried strawberries into a fine powder. Beat the frosting butter until creamy, about 2 minutes. On low speed, add the powdered sugar, frosting vanilla and milk or cream. Add the strawberry powder and frosting salt, then beat on medium until completely smooth, about 3 minutes. Add more milk if it is too stiff or more powdered sugar if it is too thin.

Trim the cooled cake layers to make flat surfaces. Set one layer on a plate or cake stand and spread buttercream over it. Add the second layer cut-side down, then frost the top and sides.