Preheat oven to 375 degrees F.
Put flour, salt, and sugar in a food processor. Pulse a few times to combine. With machine running, add cold butter, followed by ice water. When dough just comes together, turn off machine. Do not over-process. Form dough into two discs and refrigerate overnight.
Add mashed berries, sugar, and salt to a saucepan. Heat on simmer until fruit has softened, sugar has thickened, and liquid has reduced (approximately 30 minutes), stirring as needed to prevent burning. Cool overnight.
Roll out each disc to 1/4-inch thickness. Trim edges so that you have a square. Cut four rectangles out of each rolled out pastry. Spread one tablespoon jam on the top half of each of the pastry rectangles, being sure to leave edges clean. Fold the pastry from one end to the top, enclosing the jam. Using a fork, seal all edges.
Brush pop tarts with egg white and bake 30 minutes until golden brown. Cool for 15 minutes.
Mix confectioner’s sugar and jam with pinch of salt until thick, but smooth. Top each pop tart with sugar frosting. Sprinkle with hibiscus crystals and top with whole strawberry.