Preheat your oven to 400°F (200°C).

If your puff pastry is frozen, let it thaw in the refrigerator for about 30 minutes. Unroll it on a lightly floured surface and cut it into 3x3 inch squares.

In a medium bowl, mix the chopped strawberries, sugar, and vanilla extract, and allow the mixture to sit for about 10 minutes.

Place a spoonful of the strawberry mixture in the center of each puff pastry square. Fold the corners of the pastry toward the center and pinch the edges to seal.

Beat the egg in a small bowl and brush the tops of each danish with the egg wash.

Arrange the danishes on a lined baking sheet and bake in the preheated oven for 15 to 20 minutes, or until puffed and golden brown.

Allow the danishes to cool slightly before dusting with powdered sugar, if desired.

Serve the danishes warm or at room temperature.