Whisk together flour, salt, and baking powder in a large bowl. Using your hands, or a food processor, cut butter into flour until pea-sized. Add water and egg and mix until a dough forms. Next, turn dough out on a lightly floured surface and knead until smooth. Wrap in plastic wrap and refrigerate for at least 1 hour.
Once your dough is chilled and your filling is cooled, divide your dough in half and place it on a lightly floured surface. Roll one half out to ¼” thick. Using a 4.5” round cookie cutter, cut out rounds. Repeat with remaining dough.
To form your empanadas, lightly moisten outer edge of your dough round with water and place 2 tablespoons of your filling in the center. Fold in half over filling and using a fork to crimp the edges together. Repeat with remaining filling and dough.
Place empanadas on prepared baking sheets and brush with egg wash. Bake until golden, about 25 minutes.