Make the pie crust: Combine dry ingredients & butter - Add flour, salt, and sugar to a food processor or mixing bowl. Dice up the cold butter and scatter it on top. Pulse for about 10-15 seconds or until the butter is in pea-size pieces.

Add discard - Add the sourdough discard and cold water and pulse until it begins to cling to itself, about 20 seconds.

Turn out the dough & chill - Turn the dough out onto a lightly floured surface and form it into a cohesive ball. Wrap in plastic wrap and place in the fridge for 30 minutes to an hour.

Roll out the dough - Roll the chilled dough into a 12x16-inch rectangle on a lightly floured surface.

Cut into rectangles - Using a pizza cutter or sharp knife, cut the dough into eight 3x8-inch rectangles.

Add jam - Add 1 tablespoon of jam to one side of each rectangle, leaving about a ½-inch border around the edges.

Seal - Fold the empty side of the dough over the jam and press the edges together to seal. Use a fork to crimp all the way around the edges.

Egg wash and vent - Brush the tops with egg wash. Use a fork to poke a few small holes in the top of each pop tart to allow steam to escape.

Chill - Place the pop tarts on a parchment-lined baking sheet. Cover and refrigerate for 30 minutes before baking.

Bake - Bake in a preheated 425°F oven for about 20 minutes, or until lightly golden brown.

Add icing - Make the icing by combining the powdered sugar and milk in a small bowl. Drizzle over the warm pop tarts, then add sprinkles if desired.