Place flour, powdered sugar, butter, vanilla, and salt, in a food processor. Pulse until the mixture resembles a coarse meal. Add the egg whites and process just until a uniform dough is obtained. If the dough is not coming together, add a little water (1-2 teaspoons).
Shape the dough into a disk about 1 inch thick before chilling. Wrap the dough in plastic wrap and transfer it to the refrigerator for 1 to 2 hours (up to overnight). Mix the jam/jelly with the cookies/cake crumbs and freeze-dried strawberries.
Roll the dough on a floured surface to a ¼ -inch (½ cm) thickness and cut circles using a cookie cutter. Place a flat teaspoon of the filling of your choice in the center of each circle. Pinch the edges together in three places so that they meet in the middle to form a triangular cookie shape. Pinch the three corners of the triangle together firmly to seal the edges. Make sure the filling is well-enclosed.
Arrange the Hamantaschen on a baking sheet lined with parchment paper. Place the baking sheet in the freezer for 30 minutes to an hour before baking.
Preheat the oven to 350°F/180°C.
Bake for 15-20 minutes until the Hamantaschen is slightly golden. Let them cool completely.
Optional: Drizzle melted white chocolate on top, let it set, and enjoy.