Place the all-purpose flour, granulated sugar, and salt in a large mixing bowl.
Add the cold cubed butter and softened cubed cream cheese to the dry ingredients.
Using two forks or a pastry cutter, cut the butter and cream cheese into the flour mixture until the dough begins to come together.
Ensure the mixture remains cool during preparation. Do not allow the butter to melt or the dough to become warm.
Alternatively, place all crust ingredients in a food processor and pulse for approximately 1 minute, or until a dough begins to form.
Divide the dough into two equal portions.
On a lightly floured surface, shape each portion into a disk.
Wrap each dough disk tightly in plastic wrap.
Refrigerate the dough for 30 minutes.
Preheat the oven to 375°F.
Line 2 baking sheets with parchment paper or silicone baking liners.
Remove one dough disk from the refrigerator at a time.
On a lightly floured surface, roll the dough to approximately 1/8-inch thickness.
Using a 2 3/4-inch round cookie cutter, cut out 40 dough circles total.
Using a small knife, cut an X in the center of 20 dough circles, leaving enough space around the edges for sealing.
In a medium mixing bowl, combine the melted butter, firmly packed brown sugar, chopped pecans, vanilla extract, and a pinch of salt.
Stir the filling mixture until fully blended.
Arrange the 20 dough circles without X cuts on the prepared baking sheets.
Place approximately 2 tsp of filling in the center of each bottom dough circle.
Leave at least a 1/4-inch border around the edge of each dough circle to allow proper sealing.
Place the dough circles with X cuts over the filling.
Align the edges of the top and bottom dough circles.
Press the edges together gently.
Use a fork to seal the edges of each mini pie, pressing carefully around the perimeter.
In a small bowl, whisk together the egg and water until well combined.
Brush the tops of the mini pies lightly with the egg wash.
Bake for 20 to 25 minutes, or until the pies are golden brown.
Remove the baking sheets from the oven.
Transfer the pies to a wire rack.
Allow the pies to cool before serving.