1.Add the strawberries, cornstarch, and 1 tablespoon sugar to a medium bowl and toss to combine, let sit until ready to use.
2.In a stand mixer fitted with a paddle attachment, cream together the cream cheese and 1/3 cup sugar until smooth. Beat in the egg yolk, vanilla, and salt and mix until fully combined. Set aside.
3.Preheat the oven to 400°F and line 2 large baking sheets with parchment paper and set aside.
4.Unfold the two puff pastry sheets and use a rolling pin to gently roll them out to smooth out the creases. Use a pizza cutter to cut each of the sheets into 4 equally-sized squares. Transfer to baking sheet, 4 each.
5.Fold over the corners of each of the squares about an inch to create an octagon. Wet your fingers to help the dough stick together.
6.Use a medium cookie scoop to scoop the cream cheese mixture onto the center of the puff pastries. About 2 tablespoons per pastry.
7.Beat together the egg and water to create the egg wash and brush all over the pastry around the cream cheese mixture. Use a spatula to slightly flatten the dollops of cheese and spread it out. Distribute the strawberry mixture evenly on top of the cream cheese mixture.
8.Bake one baking sheet at a time for 18 to 20 minutes each, placing the other in the fridge while the first one bakes. Let cool slightly then transfer to a wire rack to cool completely. Dust with powdered sugar before enjoying.