Add the flour, sugar and salt to a food processor and pulse a few times to evenly combine. Add the butter and shortening and pulse about 8 times, just enough to cut butter into smaller pieces. With the processor running, pour ice cold water down the feed tube and pulse until the dough begins to clump together.

Turn the dough onto a floured surface and gather into a ball. Divide into 2 even portions and flatten or roll each portion into an approximate 6-inch disc and wrap tightly with plastic wrap. Chill at least one hour in the refrigerator.

Line two baking sheets with parchment paper and set aside. Remove 1 disc of dough from the refrigerator and let rest 10 minutes to soften (keep the other disc in the refrigerator).

On a lightly floured cutting board, roll the dough into a little larger than a 9x12-inch rectangle in order to create nine 3x4-inch rectangles. Cut into rectangles and transfer to baking sheets, chilling them as necessary.

Brush egg wash over the edges of each rectangle and fill with Nutella and brown sugar mixture. Seal the rectangles and freeze for 30 minutes.

Preheat the oven and brush the tops with egg wash before baking until golden.

Cool the pop tarts and glaze them before serving.