In a large bowl, sift together flour, cocoa powder, sugar, salt and baking powder.
Add butter and cream cheese to the flour mixture. Use a pastry cutter or your fingers to cut butter and cream cheese into the flour mixture until it resembles pea-sized crumbs.
Add 2 tablespoons of the cold water to the mixture. Stir gently just until the mixture begins to hold together.
Turn mixture out onto work surface. Press mixture together and fold over onto itself.
Form dough into a disk. Wrap in plastic wrap and refrigerate for 1 hour.
In a small microwavable bowl, melt chocolate chips and sweetened condensed milk in the microwave. Heat for 10 second intervals, stirring until smooth.
Set aside to cool to room temperature.
Preheat oven to 375ºF. Line a large baking sheet with parchment paper.
In a small bowl, whisk together egg and remaining 1 tablespoon water.
On lightly floured surface, roll dough to 1/8-inch thickness.
Cut out 20 circles with a 2 3/4-inch circle cutter (or cut into desired shapes of your choice).
Place 10 dough circles about 1 inch apart onto prepared baking sheet. Top each with 1 tablespoon of filling.
With a small pastry brush or your finger, brush egg mixture around the perimeter of each of the filled dough circles.
Top each with the 10 remaining dough circles. Crimp edges together with a fork. Brush pies with remaining egg mixture.
Bake for 25 minutes or until crust is crispy and browned.
Transfer to wire racks to cool. Sprinkle cooled pies with powdered sugar or drizzle with melted white chocolate.
*The chocolate chips you use depends on personal preference. Bittersweet chocolate chips give a more intense chocolate flavor, while semi-sweet chocolate chips yield a slightly sweeter finished product.