Get a head start on this by making it the day before. Store in the fridge for up to three days or in the freezer for up to three months.
1. In a small bowl, whisk together 1 of the eggs and the milk; set aside. In a medium bowl, combine 2 1/4 cups all-purpose flour and the salt. Add the butter and, with your fingertips, work it into the flour mixture until the mixture resembles coarse cornmeal. Add the milk mixture and stir until the dough comes together. Add additional flour as needed to make a soft dough. Knead a few times with the palm of your hand to fully combine. Form a disk and wrap in plastic wrap. Refrigerate for 1 hour.
2. Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper. In a small bowl, whisk together 1 egg with the water; set aside.
3. On a lightly floured work surface, divide the dough into desired number of empanadas, depending on the recipe, and roll into balls. Cover with plastic wrap to prevent drying out.
4. Add more flour to the work surface. Working with one ball at a time, roll out into a 6-inch circle. Fill with 1/4 cup filling. Lightly brush outside 1/4-inch edge of dough with egg mixture. Fold in half, seal with a fork, and transfer to the prepared baking sheet. Repeat with the remaining dough.
5. Brush the top of each empanada with the remaining egg mixture. Bake for 20 minutes or until golden brown.