Adjust baking rack to lower middle position and preheat oven to 350 F. Line a 13x18 baking sheet with parchment paper and lightly spray with baking spray. 

Remove raspberries from freezer and allow to thaw at room temperature for 15-20 minutes. Mix together raspberries, 1/2 cup granulated sugar, instant tapioca, and lemon juice together in a bowl. Set aside while you roll out the crusts. 

Unroll one package of pie crusts. There will be two round pie crusts in one box. Lightly dust a work surface with flour. Place one crust round on the counter and lightly brush the bottom third of the crust with water. Overlap the bottom third of the crust with the other crust round. Roll out both crusts together until they make one big rectangle, about 19x14". Transfer crust to a baking sheet. 

Fill the crust with the raspberry mixture and spread it out evenly. Repeat the crust process with the remaining box of crusts, and layer the crust rectangle on top of the raspberry mixture. Make sure the edges line up evenly, then cut off any excess. Pinch and crimp together, then cut some vents evenly across the crust to allow steam to escape. 

In a small bowl, whisk together the egg and one tablespoon of water. Lightly brush egg wash on top of pie crust with a pastry brush, then evenly sprinkle with one tablespoon of turbinado or granulated sugar. 

Bake pie for about 50 minutes or until the edges and top of pie are lightly browned and insides are bubbly. Allow pie to completely cool. 

Melt together butter and milk in the microwave or a small saucepan. Add powdered sugar and whisk until smooth, then drizzle over pie. Cut into squares and enjoy!