Preparing the Strawberry Cake
Preheat the oven to 350°F (175°C). Grease three 8-inch round cake pans and line the bottoms with parchment paper for easy removal.
If using whole freeze-dried strawberries, grind them into a fine powder using a food processor or spice grinder. If also making the frosting on the same day, reserve the frosting portion in a sealed container to prevent clumping.
In the bowl of a stand mixer fitted with a paddle attachment (or a large mixing bowl), combine the flour, sugar, baking powder, salt, and freeze-dried strawberry powder. Mix on medium speed for about a minute to evenly distribute the ingredients.
In a separate bowl, whisk together the whole milk, egg whites, vegetable oil, vanilla extract, and white vinegar until thoroughly blended.
With the mixer on low speed, gradually incorporate the softened butter into the dry ingredients, adding a tablespoon at a time. Continue mixing until the texture resembles coarse crumbs with no large butter pieces remaining.
Slowly add one-third of the milk mixture to the dry ingredients, mixing on low until a thick paste forms. Scrape down the sides of the bowl.
Pour in half of the remaining milk mixture and mix on medium-low speed for three minutes until the batter becomes smooth.
Add the final portion of the milk mixture along with the food coloring (if using), then beat on medium-low speed for four minutes until the batter achieves a fluffy and silky consistency.
Evenly distribute the batter among the prepared cake pans (approximately 630g per pan if making three layers). Bake for 40-45 minutes, or until the tops spring back when lightly touched. A toothpick inserted into the center should come out with a few moist crumbs.
Preparing the Strawberry Cream Cheese Frosting
In the bowl of a stand mixer, beat the softened butter until smooth. Add the cold cream cheese and continue mixing until fully incorporated and creamy.
Add the reserved freeze-dried strawberry powder and kosher salt, beating until fully combined.
Gradually add the powdered sugar, one cup at a time, mixing on low speed until incorporated. Increase the speed to medium and beat for about one minute until the frosting becomes fluffy and light.
Add heavy cream or milk, one tablespoon at a time, until the desired consistency is achieved.
Making the Strawberry Simple Syrup (Optional)
In a small saucepan, bring the water and granulated sugar to a boil, stirring until the sugar dissolves completely.
Allow the syrup to cool for 5-10 minutes before whisking in the strained strawberry puree.
Refrigerate until completely chilled before using.
Assembling the Cake
If time allows, chilling the cake layers before assembly facilitates easier frosting. Wrap each layer in plastic wrap and freeze for up to one week.
Level the cake layers as needed. If using simple syrup, brush it over each layer for extra moisture.
Spread a generous layer of strawberry cream cheese frosting between each cake layer, then coat the entire cake with a smooth layer of frosting.
Garnish with fresh strawberry slices and refrigerate the cake until ready to serve, as the frosting remains soft at room temperature.