Preheat the oven to 325°F. Grease three round 8-inch cake pans with nonstick spray and/or line with parchment rounds. (If you don’t have 3 pans, bake the first 2 layers, let the pans cool completely, then regrease the pan and bake the third layer.)
In a medium bowl, whisk together the flour, strawberries, baking powder, and salt.
In the bowl of an electric mixer fitted with the paddle attachment, beat together the butter and sugar on medium speed until light and fluffy, 2 to 3 minutes. Scrape down the sides of the bowl.
Add the egg whites in 3 separate additions, beating well after each addition. Beat in the vanilla.
Reduce the mixer speed to low and add one-third of the flour mixture. As soon as the flour disappears, mix in half of the milk, then the next third of the flour, then the milk, then the remaining flour. With each addition, stop as soon as the ingredients are incorporated.
Divide the batter between the prepared pans. Bake until a toothpick inserted into the center comes out mostly clean with just a few moist crumbs clinging to it, 20 to 25 minutes. Transfer the cakes from the pans to a wire rack to cool completely.
While the cakes cool, make the frosting: With an electric mixer on medium-high speed, beat together the cream cheese and butter until light and fluffy, about 3 minutes. Beat in the vanilla and salt. Reduce the speed to low and gradually add the powdered sugar, mixing until smooth and fluffy.
With a serrated knife, trim the domed top off of each cake layer to create a flat surface (eat the crumbs or mix them into ice cream, mmmmm).
Frost the cake: Place the first layer on a cake stand. Tuck strips of parchment paper or wax paper underneath the edges to keep the plate tidy. Cover the top of the first layer with frosting. Place a second cake layer on top of the first and cover it with frosting. Place the third on top and cover with frosting.
Make a crumb coat: Spread a very thin layer of frosting all over the whole cake and let it set a minute or two (you’ll still see cake peeking through). Refrigerate for 10 minutes. This will make the rest of the process much easier, trust me.
Wipe your knife clean, then frost the entire cake’s top and edges with the remaining frosting so it’s completely covered. Decorate as desired.
Notes
*The best way to crush your strawberries is in a spice grinder, but a mortar and pestle, mini food processor or mashing them in a zip-top bag will also work.
*If you want a totally, bake-sale-winning smooth texture, sift the strawberries after mashing. (I don’t mind the specks of some larger pieces in the cake and leave as is)
*You can also use freeze-dried raspberries, the color might be slightly different
You will have extra frosting left from the cake. You can either frost it more thickly (be warned that it is fairly sweet), or save the frosting for another use (dipping with pretzels anyone?)
TOSTORE: This cake will last in the refrigerator for 5 days. Cover it in plastic wrap or transfer slices to an airtight container.
TO FREEZE: Fully frosted or unfrosted cake can be frozen for up to 2 months—let thaw overnight in the refrigerator, then bring to room temperature prior to serving.
TO MAKE AHEAD: The cake layers can be baked 1 day in advance—cool completely, then wrap airtight and store at room temperature. Frosting can be prepared 1 day in advance—place in an airtight container and store in the refrigerator.