Prepare Dough: In a large mixing bowl, whisk together flour, sugar, and salt. Cut in cold butter until resembling coarse crumbs. Add ice water until dough forms. Wrap in plastic and refrigerate for at least 30 mins.

Make Filling: In a bowl, mix blueberries, sugar, and vanilla. Mash some blueberries to create a chunky texture. Set aside.

Roll Out Dough: Flour your surface and divide the dough. Roll to 1/8 inch thick. Cut into 3x4 inch rectangles and transfer to a baking sheet.

Assemble Pop Tarts: Place filling on half of the rectangles, top with the other half, seal edges, and make slits for steam.

Bake: Preheat oven to 375°F. Brush tops with egg wash and bake for 20-25 mins until golden and filling bubbles.

Glaze & Serve: Mix powdered sugar with milk/water. Drizzle over cooled pop tarts and serve warm or at room temperature.