Preheat oven to 350°F (177°C). Line a 12-count muffin pan with cupcake liners. This recipe makes 16-17 cupcakes, so you will have a few cupcakes to bake in a 2nd batch. Please read notes about mini cupcakes.
Slice 5 strawberries and place in a food processor or blender. Pulse until strawberries are a chunky puree. You should have about 1/3 cup. Set aside. Finely chop remaining strawberries. Set aside.
With a handheld or stand mixer fitted with a whisk attachment, beat the 3 egg whites on high speed in a medium bowl until soft peaks form, about 2-3 minutes. Set aside.
Make the cupcakes: Sift the flour, cornstarch, baking powder, and salt together in a large bowl. Set aside. Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on high speed until smooth and creamy – about 1 minute. Add the sugar and beat on high speed for 3-4 minutes until creamed together fairly well. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. Add the egg yolk and vanilla and beat on medium-high speed until combined. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. With the mixer on low speed, add the dry ingredients in three additions alternating with the whole milk, beginning and ending with the dry ingredients, and mixing each addition just until incorporated. Do not overmix. Fold egg whites, 1/3 cup strawberry puree, and finely chopped strawberries into the cupcake batter. The batter will be velvety and slightly thick.
Spoon batter into cupcake liners filling halfway. Bake for 20-24 minutes or until the tops of the cupcakes spring back when gently touched and a toothpick inserted in the center comes out clean. Allow to cool in the pan for 5 minutes, then transfer to a rack to cool completely.
Make the frosting: Using a blender or food processor, process the freeze-dried strawberries into a powdery crumb. You should have around 1/2 cup. Set aside. With a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy – about 2 minutes. Add confectioners’ sugar, strawberry powder, cream, and vanilla extract with the mixer running on low. Increase to high speed and beat for 3 full minutes. Add 1/4 cup (30g) more confectioners’ sugar if frosting is too thin or 1 more Tablespoon of cream if frosting is too thick. Add a pinch of salt if frosting is too sweet. Frost cupcakes as desired. I used a Wilton 1M piping tip. Leftover prepared cupcakes can be stored covered tightly at room tempe