For the Strawberry Smash: In a large bowl, smash together the strawberries, sugar, and lemon juice using a handheld potato masher, or a large fork. You want to leave the mixture a little chunky, but you want the juices to release and the sugar to dissolve. Sift in the cornstarch and mix until no clumps remain. Place in the fridge while you make the cupcakes. For the Cupcakes: Preheat oven to 350°F. Line 2 or 3 standard muffin trays with paper liners; set aside. In a medium bowl, combine the flour, baking powder, and salt; set aside. In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites on high until stiff peaks form, about 8 minutes. Gradually beat in the sugar. Add in the egg yolks, one at a time, followed by the vanilla. Alternately add in the flour and milk, beginning and ending with the flour. Fill the paper liners ¾ of the way full (I find it’s easiest to fill them with a large cookie scoop). Bake for 20-25 minutes, until set in the centers and lightly golden. For the Tres Leches Mixture: In a bowl, whisk together all of the tres leches mixture ingredients, until combined. Using a skewer, poke multiple holes in each cupcake. Spoon about 1 tablespoon of the mixture over each cupcake, and place in the fridge for 2 hours. Spoon 2 teaspoons of the strawberry smash over each cupcake, and top with a 1-2 tablespoon-sized dollop of whipped cream.