Preheat the oven to 350 degrees F. Add the sliced strawberries to a parchment-lined baking sheet. Sprinkle 2 tablespoons of sugar onto the strawberries. Toss them gently then roast in the the oven for 20 minutes. Remove from oven and allow to cool for 5 minutes. Add the strawberries to a blender or food processor and puree until smooth. You should end up with about 1/2 cup puree.
Keep the oven at 350 degrees F. Grease two 8-inch cake pans. Set aside. (See notes for sheet cake)*
In a medium bowl, whisk the flour, baking powder, baking soda, and salt.
In the bowl of an electric mixer fitted with the paddle attachment, beat butter on low speed until smooth and creamy. Add sugar and beat on medium-low speed until light and fluffy, about 8-10 minutes.
In a large measuring cup, whisk together the strawberry puree, buttermilk, egg whites, and vanilla until well combined.
On low speed, add 1/3 of the dry ingredients to the butter/sugar mixture, then half of the wet. Add half of the remaining dry, then liquids. Finish with remaining dry ingredients. Beat until smooth.
Pour the batter in the prepared cake pans and bake for 30-35 minutes, or until a skewer inserted into the center comes out clean.
Allow the cake layers to cool in the pan for 10 minutes, then transfer them onto a cooling rack and cool to room temperature.
To make the frosting, add sliced strawberries and freeze dried strawberries to blender or food processor. Puree until smooth. Set aside. In your stand mixer fitted with the paddle or whisk attachment, beat the cream cheese and butter on high speed for about 1 minute, or until smooth and creamy. Beat in the strawberry puree. Gradually add the powdered sugar and salt. Beat on medium-high speed until completely smooth and fluffy.
Assemble the cake: Use a large serrated knife to slice a thin layer off of the top of the cakes to create a flat top. Place 1 cake layer onto your cake stand and evenly spread a layer of frosting. Top with 2nd layer and spread the remaining frosting over the top and sides of cake. Sprinkle top with crumbled freeze dried strawberries. Refrigerate until ready to serve.
To bake in a 9×13 sheet pan – pour the batter into a greased 9×13 baking pan and bake for 30-40 minutes or until a toothpick inserted in the center comes out clean. Cool, then frost the top of cake.