Using a food processor, fitted with the metal blade, add the flour, cocoa and salt to the bowl, whisk together, then add 3/4 cup (170 grams) cold butter cut in cubes and pulse until butter is absorbed (about 10 to 12 one second pulses), then add the remaining cold butter (cubed) and pulse two or three times (no more) to combine, add the cold water and pulse four or five times just until the dough comes together to form a ball (really important not to over process).
Add the cold water and pulse just until the dough comes together to form a ball (really important not to over process). You will see bits of butter throughout the dough, this is what makes it flaky.
On a lightly floured surface place dough and knead lightly approximately 10 times. With a lightly floured rolling pin (lightly flour the dough so it doesn't stick) roll into a rectangle approximately 12 x 18 inches (30 x 45 cm).
Fold the dough in half and then half again and one last time, wrap in plastic and refrigerate for 1 - 2 hours (I left mine in the fridge for two hours).
Remove the dough from the fridge, divide into 2 parts, one part roll into a circle and cut into 8 triangles, roll up crescent style and place on a parchment paper lined cookie sheet.
The other part roll into a rectangle or square and cut into rectangles, place 2-3 squares of chocolate, roll and place on a parchment paper lined cooke sheet.
The leftovers can be cut and twisted. Chill the dough again while the oven is pre-heating.
Pre-heat 375F (190C).
Brush the dough lightly with an egg wash and bake for approximately 15-20 minutes. Let cool on wire rack before serving.
EGG WASH
In a small bowl beat together the egg and water until well combined.