Place the sifted flour, salt, and cold cubed butter in a mixing bowl. Use a pastry cutter or fingertips to cut in the butter until the mixture resembles coarse crumbs with some pea-sized pieces.
Gradually add the cold water, a tablespoon at a time, mixing gently until the dough begins to come together. Avoid overworking to keep the pastry flaky.
Gather the dough into a ball, flatten into a disk, wrap with plastic wrap, and refrigerate for at least 30 minutes to relax the gluten.
Meanwhile, prepare the strawberry filling by combining chopped strawberries, sugar, and lemon juice in a bowl. Toss gently and set aside to macerate until the strawberries release their juices, about 15 minutes.
Once chilled, roll out the dough on a lightly floured surface into a rectangle about 1/8-inch thick. Fold and turn the dough a quarter turn, then repeat rolling to create thin, layered sheets.
Cut the dough into equal squares or rectangles, then place a spoonful of strawberry filling in the center of each piece.
Fold the pastry over the filling to form a sealed pocket, pressing the edges gently to secure. Optionally, crimp with a fork for decoration.
Arrange the filled pastries on a baking sheet lined with parchment. Brush their tops lightly with an egg wash or milk for a golden finish.
Bake in a preheated oven at 375°F (190°C) until the pastries are golden brown and crispy, about 20 minutes. Let them cool slightly before handling.
While the pastries cool, whip the chilled heavy cream with powdered sugar until soft peaks form, creating a light and fluffy topping.
Serve the warm or cooled strawberry pastries topped with a dollop of the sweetened whipped cream, enjoying the contrast between flaky crust, juicy strawberries, and creamy topping.
