• Add the flour and salt to a food processor and combine. Add the cold, cubed butter and pulse until the mixture resembles coarse crumbs.
• Add the discard and vinegar and pulse until the dough forms a cohesive ball. The dough will not be smooth like bread dough but more tacky like biscuit dough. If too dry, add ice water a teaspoon at a time until it just comes together. If sticky, add a bit of flour and pluse to integrate.
• Transfer the dough onto a clean surface and use your hands to shape the dough into a rectangle. It doesn't have to be perfect, a rough rectangle wil do.
• Wrap the dough in plastic and refridgerte for at least 1 hour. *You can leave the dough in the fridge for up to 48 hours for a long-fermented version.
• Preheat the oven to 350°F (177°C). Line a baking sheet with parchment.
• Roll the dough to about ⅛" thickness. Cut into four strips. Add about 1-2 tablespoons of jam to one side of each strip, leave some space along the sides, fold over, and press the edges to seal. You can also brush an egg wash on the edges to make them seal better, or just a wet finger run along the lines can help!
• Place pastries on the prepared baking sheet and bake for about 25 minutes or until golden. Transfer to a cooling rack.

For the Glaze

• In a mixing bowl whisk the powdered sugar, lemon juice, and water together until smooth.
• Drizzle the glaze over the cooled pastries. Make sure to wait until they are completely cool or the glaze will not adhere to the pop tarts well.