Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.

In a large bowl, whisk together the flour, sugar, baking powder, and salt. Add the cold, cubed butter and mix until the mixture resembles coarse crumbs.

In a separate bowl, combine the softened cream cheese, milk, and vanilla extract. Stir until smooth, then add to the flour mixture. Mix until just combined.

Turn the dough out onto a lightly floured surface and knead gently until it comes together. Roll the dough into a rectangle about 1/4 inch thick.

In a small bowl, mix the sliced strawberries with lemon juice and cornstarch. Set aside to let the juices combine.

Cut the rolled dough into squares (about 4x4 inches). Place a spoonful of the strawberry mixture in the center of each square. Fold the corners of the dough over the filling to create a pocket and pinch to seal.

Place the filled pastries on the prepared baking sheet. Brush the tops with the beaten egg for a golden finish.

Bake for 20-25 minutes or until golden brown. Remove from the oven and let cool slightly.

Dust with powdered sugar before serving.