Make Pastry:

1. Add the flour and salt to the bowl of a food processor. Pulse 2-3 times until combined.
2. Add in the butter and pulse 7-9 times, until the butter is broken down into small pea-sized pieces.
3. Add the vinegar to the water. With the motor running, slowly pour the water mixture into the flour mixture. When finished adding the water, the dough should be crumbly and it should hold together when squeezed. Drip in more water and toss together if needed. Do not overprocess the dough until it clumps around the blade.
4. Empty the mixture onto a work surface and divide it into two equal piles.
5. Quickly press each dough pile together. If there are any dry spots, drip a bit more water onto them and knead together if you have to.
6. Place each dough in a piece of plastic wrap and wrap tightly.
7. Using a rolling pin, roll the dough out until it stretches to the edges of the plastic wrap.
8. Refrigerate for at least 2 hours, but preferably overnight.

Make Turkey Filling:

1. In a Dutch oven, heat the oil over medium heat. Once hot, add the onion and salt and cook until the onion is beginning to soften about 5 minutes.
2. Add in the butter, flour, thyme, and pepper. Cook, stirring often, until the butter has fully melted. Slowly whisk in the stock, about ½ cup at a time, until it is all combined. Heat the sauce to a boil, then reduce the heat to a simmer.
3. Add in the leftover turkey and veggies (if using frozen veggies, wait to add them until the next step) and simmer, stirring occasionally, for 20 minutes.
4. Shut off the heat, stir in 1 teaspoon of the vinegar, then season to taste with more vinegar, salt, and pepper as needed. (If using frozen veggies, add them here.)
5. Transfer the filling to a shallow container and let cool completely at room temperature or overnight in the refrigerator.

Assemble and Bake:

1. Line two rimmed baking sheets with parchment paper and set aside.
2. Remove the dough from the refrigerator. On a well-floured work surface, roll out one piece of dough to a rough rectangle about 10-by-16 inches, or about 1/8-inch thick. Using a pastry wheel or a knife, cut out twelve 3-by-4-inch rectangles. Repeat with the second dough. Then gather the scraps together and roll out the dough in the same manner, cutting out as many 3-by-4-inch rectangles as possible. This dough should yield 24 rectangles total. If the dough is extremely warm at the end of this process, place the rectangles in the freezer briefly to firm up.
3. Working with one dough rectangle at a time, brush a thin coating of eggwash onto the outer edge. Place a scant ¼ cup of turkey filling in the middle. Place a second dough rectangle over the top and press down on the edges to seal the two pieces together.
4. Using a fork, press down to seal the edges. Finally, using a pastry bench scraper, press down to cut off the edges on all sides of the pastry. This makes the final product look neat and adds extra security to keep it sealed. Repeat filling and shaping the hand pies with the remaining dough rectangles and filling (you’ll make 12 hand pies total).
5. Place the hand pies spaced evenly apart on the two prepared baking sheets. When finished, place the baking sheets into the refrigerator or freezer to chill while the oven preheats.
6. Preheat the oven to 425ºF and set racks in the middle and lower parts of the oven. Remove the pies from the refrigerator or freezer and brush the tops with the remaining egg wash.
7. Bake in the oven for 35 minutes or until the pie dough is lightly golden all over.
8. Transfer the hand pies to a wire rack to cool for 5 minutes before serving.