01 - In a large bowl, combine flour, salt, and sugar. Add cold cubed butter and, using a pastry cutter or your fingertips, cut it into the dry mixture until it resembles coarse crumbs with some pea-sized butter pieces remaining.
02 - Drizzle in cold water and mix gently until the dough just comes together. Do not overwork. Divide into 2 equal disks, wrap tightly in plastic, and refrigerate for at least 30 minutes.
03 - Preheat oven to 375°F (190°C). Line two baking sheets with parchment paper.
04 - On a lightly floured surface, roll out one dough disk to about 1/8-inch (3 mm) thickness. Cut into 3x3-inch (7.5 cm) squares.
05 - Place a teaspoon of chopped chocolate in the center of each square. Fold two opposite corners over the filling, slightly overlapping, and gently pinch to seal—resembling a mini croissant shape.
06 - Arrange shaped cookies on the prepared baking sheets. Brush tops generously with beaten egg and sprinkle with turbinado or granulated sugar.
07 - Bake for 13–15 minutes until golden brown and crisp. Transfer to a wire rack to cool before serving.
08 - Repeat the rolling, filling, shaping, and baking process with the second dough disk and remaining chocolate filling.