Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
In a bowl, combine the sliced strawberries, granulated sugar, and cornstarch. Stir until the cornstarch fully melts into the strawberries. Set aside
In a separate bowl, combine the softened cream cheese, powdered sugar, and vanilla extract. Mix with a hand held mixer until completely smooth and silky. Set aside.
Unfold the thawed puff pastry onto a lightly floured surface. Use a pizza cutter to cut the sheet into 4 equal squares.
Spoon a generous dollop of the cream cheese mixture onto the center of each square. Spread slightly, leaving a small border between the filling and the edges of the dough.
Spoon the strawberry mixture on top of the cream cheese layer.
Fold the corners of each square toward the center, slightly overlapping to create an envelope shape as shown in the photos. Press the edges gently to seal.
Brush the exposed dough border (areas without filling) with melted butter, then apply the egg wash over the entire top for a golden finish.
Bake for 15 minutes, or until the danishes are puffed and deep golden brown.
Remove from the oven and cool on the baking sheet for a few minutes, then transfer to a wire rack. Dust with powdered sugar if desired. Enjoy!