1. Preheat your oven to 375 F (190 C). Line a baking sheet with parchment paper. This prevents sticking and makes cleanup a breeze.

2. In a small bowl, gently stir together the sourdough discard and your chosen fruit preserves. This creates a unique, slightly tangy filling.

3. Open the can of crescent roll dough. Unroll the dough and separate it into four rectangles. You might need to gently pinch together the perforations where the triangles meet to form a solid rectangle.

4. Spoon about 1-2 tablespoons of the sourdough-preserve mixture onto the center of two of the dough rectangles, leaving a small border around the edges.

5. Place the remaining two dough rectangles on top of the filled ones. Gently press down around the edges to seal them. Use a fork to crimp the edges, creating a decorative seal and ensuring the filling stays inside.

6. In a small bowl, mix the granulated sugar and ground cinnamon. Brush the tops of each pop tart with milk, then sprinkle generously with the cinnamon-sugar mixture. This will give them a beautiful golden crust and extra flavor.

7. Transfer the pop tarts to your prepared baking sheet. Bake for 10-12 minutes, or until the pastry is puffed and golden brown. The edges should look crisp, and the tops will have a lovely caramelized appearance from the sugar.

8. Let the pop tarts cool on the baking sheet for a few minutes before transferring them to a wire rack. They are best enjoyed warm, but also delicious at room temperature.