Step 1

In a medium-sized mixing bowl, whisk the flour, sugar and salt. Grate the cold butter, using a cheese grater, into the flour mixture. Use a bench scraper or a pastry cutter to cut the butter into the flour until it forms large crumbles.

Step 2

Add the sourdough starter discard and vinegar to the mixture and use a fork to bring the dough together. Use your hands to bring the mixture into a cohesive ball and press into a rectangular shape. (Add a teaspoon of cold water if the mixture is too dry.)

Step 3

Wrap the dough in plastic wrap and use a rolling pin to flatten the dough and smooth the edges. Let the dough chill in the fridge for at least one hour. (Up to 24 hours)

Step 4

Preheat your oven to 350°F (177°C) and line a baking sheet with parchment paper.

Step 5

Roll the dough into a rectangle, with a 1/8' thickness, on a lightly floured surface. Cut the dough into 4 long strips. Brush the edges with the egg wash.

Step 6

Add 2 tablespoons of filling to one side of each rectangle and fold the dough over itself. Use a fork to press and seal the edges. Brush the egg wash over the top of each pop tart.

Step 7

Place the pop tarts onto the baking sheet and bake for 25-30 minutes or until the crust is golden brown. Remove from the oven and transfer the baked pop tarts to a cooling rack.

Step 8

In a small bowl, whisk the powdered sugar and water together until thick and smooth. Pour onto each pop tart and sprinkle with coarse sugar or sprinkles.