In a food processor, combine all-purpose flour and salt, then add cold butter cut into small cubes. Pulse until the mixture resembles coarse crumbs. Introduce the sourdough discard and apple cider vinegar, continuing to pulse until a tacky dough forms. Chill the dough for at least 1 hour.

Once the dough has chilled, preheat your oven to 350°F (177°C) and prepare a baking sheet lined with parchment paper.

On a lightly floured surface, roll out the chilled dough to ⅛ inch thick. Cut into 3x4 inch squares.

Spoon 1-2 tablespoons of jam onto one half of the dough square, fold over, and seal the edges.

Brush with egg wash and bake for about 25 minutes or until golden.

Whisk together powdered sugar, lemon juice, and water until smooth, then drizzle over cooled pastries.