In a large bowl, whisk together the flour and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs.

Gradually add the ice water, mixing until the dough just comes together. Form into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

In a bowl, combine the mixed berries, sugar, cornstarch, and lemon juice. Gently toss to combine.

On a lightly floured surface, roll out the dough to about 1/8 inch thickness. Cut out circles or desired shapes using a cookie cutter or knife.

Place a spoonful of the berry filling in the center of half of the dough circles. Top with another circle of dough and crimp the edges to seal.

In a small bowl, whisk together the egg and milk to create an egg wash. Brush the tops of the hand pies with the egg wash and sprinkle with sugar.

Bake in a preheated oven at 375°F (190°C) for 20-25 minutes, or until golden brown.

Let cool slightly before serving.