Sift the flour and salt onto the work surface. Make a well in the flour. Add the cold water and make a paste using your fingertips, make a paste. Add the melted butter and work into the paste until a rough dough has been created; form it into a square block. With a sharp knife, cut an X on the top and about half way through the block, this help to cut the gluten strands so that they can relax more quickly. Cover the dough with plastic film and refrigerate.
When the detrempe has rested at least 30 minutes, take the butter (beurrage) out of refrigerator. Plate it between 2 sheets of plastic film and beat it to flatten with a rolling pin. The butter should become pliable without any lumps to it, but should still be very cool. Form it into a square block.
Take out detrempe, which should be the same consistency of beurrage. Roll the detrempe slightly to make a square, large enough so that it will able to enclose the butter.
From this point on, be sure to use sufficient flour when rolling and turning the dough; it must not stick to work surface.
Place the butter over the detrempe, so that it looks like a diamond inside a square. Fold the edges of the dough over the butter to enclose it and pinch it lightly to seal.
Press the dough with a rolling pin 4 to 5 times along its length until it gets to approximately 9 inches. Then, using flour to dust the work surface, roll it to 22 inches long
Brush off any excess flour and fold the dough into third. Repeat step 6. The dough now has 2 turns, wrap it with plastic film and refrigerate for 30 minutes. Take it out, do another 2 turns, mark the dough to 4 turns, wrap it and refrigerate for another 20 minutes.
Take the dough and make the last 2 turns, refrigerate to rest before use, or freeze it for future use.