1. 1. Prepare the Dough Base: In a large mixing bowl, combine the softened butter, granulated sugar, vanilla extract, and salt. Beat with an electric mixer on medium speed until light and fluffy, about 2-3 minutes.

2. 2. Incorporate Sourdough Discard and Flour: Add the sourdough discard to the butter mixture and mix until just combined. Gradually add the all-purpose flour, mixing on low speed until a crumbly dough forms.

3. 3. Bring the Dough Together: Slowly add the cold water, one tablespoon at a time, mixing until the dough just comes together. Be careful not to overmix. The dough should be soft but not sticky. Form the dough into a disc, wrap it in plastic wrap, and refrigerate for at least 30 minutes.

4. 4. Roll and Cut the Dough: On a lightly floured surface, roll out the chilled dough to about 1/8-inch thickness. Using a rectangular cookie cutter (about 2×3 inches) or a knife, cut out an even number of rectangles. You can gather and re-roll scraps once or twice.

5. 5. Assemble the Hand Pies: Place half of the dough rectangles on a parchment-lined baking sheet. Spoon about 1-2 teaspoons of your chosen fruit preserves onto the center of each rectangle, leaving a small border around the edges. Top with the remaining dough rectangles.

6. 6. Seal and Vent: Gently press down the edges of each hand pie with your fingers, then use the tines of a fork to crimp and seal them securely. This also creates a decorative edge. Use a small knife or a fork to poke 2-3 small holes on the top of each hand pie to allow steam to escape during baking, preventing them from puffing up too much.

7. 7. Bake to Golden Perfection: Preheat your oven to 375 F (190 C). Bake the hand pies for 15-20 minutes, or until the crust is lightly golden brown and flaky. The exact time will depend on your oven.

8. 8. Prepare and Apply Icing: While the hand pies cool slightly, whisk together the powdered sugar with 1-2 tablespoons of milk or water until you reach a smooth, pourable consistency. Drizzle the icing over the warm (but not hot) hand pies. If desired, immediately add sprinkles before the icing sets.