In a stand mixer fitted with the paddle attachment, mix the all-purpose and cake flours, salt, and butter on low speed for about 30 seconds, just until the flour is coated with butter. There will still be large chunks of butter, about ¼ inch / 6mm thick or larger.

Add the chilled water in a steady but slow stream while mixing, just until the dough starts to form small clumps and there is little flour left in the bowl. If you reach into the bowl and the dough comes together when you squeeze it, it's done. If it crumbles with dry powdery bits, sprinkle in a bit more water.

Turn the dough out onto a lightly floured work surface and using a bench scraper, fold and push the dough into a rectangle. It will be a bit shaggy looking and that's just right. Flour the surface as you work to prevent the dough from sticking too much. Flour the top of the dough and roll it out into a rectangle that measures 10 by 15 inches / 25 by 38cm. Brush off any excess flour with a clean and dry pastry brush. Using a bench scraper to help you lift the dough, fold one-third of the dough into the center. Fold the other one-third over the top, like a letter.

Turn the dough and roll it out again to a rectangle that measures 10 by 15 inches / 25 by 38cm, remembering to add enough flour to prevent sticking. Repeat the brushing and folding technique. The dough will start to be less shaggy and start to look like a cohesive dough.

Turn the dough and repeat all the rolling, brushing, and folding steps for the third time. If the dough is getting too sticky with butter, you can cover it and refrigerate for about 20 minutes to create a more workable dough.

Turn the dough and do the fourth and final set of rolling, brushing, and folding. The dough should now be smooth and look like a clean rectangle of dough. Divide it in two; you can use the dough right away or cover and refrigerate it for a few days. You can also freeze the dough for about 1 month.